Angular extract i18n and merge

This extends Angular CLI to improve the i18n extraction and merge workflow.
New/removed translations are added/removed from the target translation files and translation states are managed.
Additionally, translation files are normalized (whitespace, stable sort) so that diffs are easy to read
(and translations in PRs might actually get reviewed ;-) ).

> [!TIP]
> If you'd like to keep your translation process simple and rather validate translations, then waiting for actual translations, I'd like you to check out doloc.io.
>
> Created by the maintainer of ng-extract-i18n-merge (@daniel-sc),
> it integrates seamlessly with this library (see here) and provides instant translations on extraction!
>
> Expect great translations!

Install

_Prerequisites_: i18n setup with defined target locales in angular.json - as
documented here.

``shell
ng add ng-extract-i18n-merge
`

$3

Run ng update ng-extract-i18n-merge@2 to upgrade from v1 to v2. This migration
switches to Angular's built-in extract-i18n builder and changes some defaults
(see breaking changes below).

If you plan to upgrade from v1 straight to v3 you must first upgrade to v2 using
the command above and then run ng update ng-extract-i18n-merge again for the
v3 update.

Breaking changes:

* Now this plugin uses the default Angular extract-i18n target - so you can
simply run ng extract-i18n.
* Default sort is now stableAppendNew (was idAsc).
* Leading/trailing whitespaces are normalized (collapsed to one space) but not
completely trimmed.
* The provided npm run script was removed (you can create your own if needed).

$3

Run ng update ng-extract-i18n-merge to update to v3.0.0 using the Angular update mechanism.
This release drops support for Angular 19 and older.
The defaults for prettyNestedTags and sort changed to false and "stableAlphabetNew" respectively.
builderI18n now defaults to @angular/build:extract-i18n instead of @angular-devkit/build-angular:extract-i18n.
During ng update existing builder configurations are updated to keep the previous behaviour (except for builderI18n, where the new default is best for most setups).

Usage

`shell
ng extract-i18n # yes, same as before - this replaces the original builder
`

$3

In your angular.json the target extract-i18n that can be configured with the following options:

| Name | Default | Description |
|----------------------------------------------------------------------------------------------------------------------------------------------------|-------------------------------------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
| buildTarget | Inferred from current setup by ng add | A build builder target to extract i18n messages in the format of project:target[:configuration]. See https://angular.io/cli/extract-i18n#options |
| format | Inferred from current setup by ng add | Any of xlf, xlif, xliff, xlf2, xliff2 |
| outputPath | Inferred from current setup by ng add | Path to folder containing all (source and target) translation files. |
| targetFiles | Inferred from current setup by ng add | Filenames (relative to outputPath of all target translation files (e.g. ["messages.fr.xlf", "messages.de.xlf"]). |
| sourceLanguageTargetFile | null | If this is set (to one of the targetFiles), new translations in that target file will be set to state="final" (instead of default state="new"). This file can be used to manage changes to the source texts: when a translator updates the target, this tool will hint the developer to update the code occurrences. |
| sourceFile | messages.xlf. ng add tries to infer non default setups. | Filename (relative to outputPath of source translation file (e.g. "translations-source.xlf"). |
| removeIdsWithPrefix | [] | List of prefix strings. All translation units with matching id attribute are removed. Useful for excluding duplicate library translations. Cannot be used in combination with includeIdsWithPrefix. |
| includeIdsWithPrefix | [] | List of prefix strings. When non-empty, only translations units with matching id are included. Useful for extracting translations of a single library in a multi-library project. Cannot be used in combination with removeIdsWithPrefix. |
| fuzzyMatch | true | Whether translation units without matching IDs are fuzzy matched by source text. |
| resetTranslationState | true | Reset the translation state to new/initial for new/changed units. |
| prettyNestedTags | false | If source/target only contains xml nodes (interpolations, nested html), true formats these with line breaks and indentation. false keeps the original angular single line format. Note: while true was the historic implementation, it is _not_ recommended, as it adds whitespace between tags that had no whitespace in between and increases bundle sizes. |
| selfClosingEmptyTargets | true | If false empty target nodes are non self-closing. |
| sortNestedTagAttributes | false | Attributes of xml nodes (interpolations, nested html) in source/target/meaning/description can be sorted for normalization. |
| collapseWhitespace | true | Collapsing of multiple whitespaces/line breaks in translation sources and targets. This handles changed leading/trailing whitespaces intelligently - i.e. updates the target accordingly _without_ resetting the translation state when only leading/trailing whitespace was changed. |
| trim | false | Trim translation sources and targets. |
| includeContext | false | Whether to include the context information (like notes) in the translation files. This is useful for sending the target translation files to translation agencies/services. When sourceFileOnly, the context is retained only in the sourceFile. |
| includeContextLineNumber | true | If includeContext has been included allow the inclusion of line number to be optional. This can help reduce noise in the committed xlf files for strings that have not changed but their line number was shifted due to other changes in the file. |
| includeMeaningAndDescription | true | Whether to include the meaning and description information in the translation files. |
| newTranslationTargetsBlank | false | When false (default) the "target" of new translation units is set to the "source" value. When true, an empty string is used. When 'omit', no target element is created. |
| sort | "stableAlphabetNew" | Sorting of all translation units in source and target translation files. Supported:
"idAsc" (sort by translation IDs),
"stableAppendNew" (keep existing sorting, append new translations at the end),
"stableAlphabetNew" (keep existing sorting, sort new translations next to alphabetical close IDs). |
| builderI18n | "@angular/build:extract-i18n" | The builder to use for i18n extraction. Any custom builder should handle the same options as the default angular builder (buildTarget, outputPath, outFile, format, progress). |
| verbose | false` | Extended/debug output - it is recommended to use this only for manual debugging. |

Contribute

Feedback and PRs always welcome :-)

Before developing complex changes, I'd recommend opening an issue to discuss whether the indented goals match the scope of this package.