#2180: Add *_EXTRA_PLUGINS variable to install extra IDE plugins per user

[Paras14]

This PR fixes #2180

Implemented changes:

• Added the tool-specific variable «TOOL»_EXTRA_PLUGINS (e.g. VSCODE_EXTRA_PLUGINS=eslint,cpp-tools,docker) allowing a user to activate additional plugins without modifying the shared project settings.
• Values refer to the filename of the plugin properties file without the .properties extension, not to the id inside it. Unresolvable entries are skipped with a warning so a single stale entry cannot break the installation of the remaining plugins.
• Implemented in PluginBasedCommandlet.getPlugins() rather than in a specific IDE commandlet, so it applies to Eclipse, VSCode and all IntelliJ-based IDEs. Plugins activated this way are reinstalled automatically when plugins are purged, unlike plugins installed manually in the IDE.
• Documented in documentation/plugin.adoc and documentation/variables.adoc.
• Note: removing an entry from «TOOL»_EXTRA_PLUGINS does not uninstall the plugin (the marker file survives). This is documented; resetting is done via --force-plugin-reinstall.

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Testing instructions

1. Build and activate this branch locally: export IDE_ROOT=/your/ide/root && ./build-local-dev.sh (revert afterwards with ideasy upgrade --mode=stable).
2. In any IDEasy project, run ide vscode and note a plugin logged as Omitting installation of inactive plugin icons (...), plus the plugin count in the Install plugin ... (n/m) steps.
3. Add to $IDE_HOME/conf/ide.properties:
   VSCODE_EXTRA_PLUGINS=icons
4. Run ide vscode again. Expected: Start: Install plugin icons (n/m) with m one higher than in step 2, and the extension present under $IDE_HOME/plugins/vscode. The shared settings/ directory is untouched (git status inside it stays clean).
5. Replace the value with the plugin's id instead of its filename, e.g. VSCODE_EXTRA_PLUGINS=vscode-icons-team.vscode-icons, and run again. Expected: a warning that the plugin is undefined, and icons is not installed, the variable takes filenames only.
6. Set VSCODE_EXTRA_PLUGINS=icons,typo-does-not-exist and run again. Expected: one warning for the unknown entry, icons installs anyway.
7. The same works for other IDEs, e.g. INTELLIJ_EXTRA_PLUGINS=watchers (close IntelliJ first, IDEasy calls idea64.exe to install plugins).

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[Ali-Shariati-Najafabadi]

Nice work, this does exactly what #2180 asked for and it's implemented generically so it covers Eclipse, VSCode and the IntelliJ based IDEs. I pulled the branch, built it and ran PluginBasedCommandletTest locally and all tests pass.

[hohwille]

@Paras14 thanks for your PR. Great work that you implemented this feature including a proper JUnit test with its own test-project. Nice job 👍
I should have already reviewed the story to question the variable name before implementation but I am always short on time so things just happen.
Also I left a design improvement proposal that I hope you can implement without much effort to further improve. Thanks in advance.

[coveralls]

Coverage Report for CI Build 32478854936

Coverage decreased (-0.002%) to 73.563%

Details

• Coverage decreased (-0.002%) from the base build.
• Patch coverage: No coverable lines changed in this PR.
• 13 coverage regressions across 3 files.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

13 previously-covered lines in 3 files lost coverage.

File	Lines Losing Coverage	Coverage
com/devonfw/tools/ide/tool/plugin/PluginBasedCommandlet.java	11	87.66%
com/devonfw/tools/ide/tool/ide/IdeToolCommandlet.java	1	78.69%
com/devonfw/tools/ide/version/VersionSegment.java	1	91.08%

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Coverage Stats

Relevant Lines:	17780
Covered Lines:	13682
Line Coverage:	76.95%
Relevant Branches:	7881
Covered Branches:	5195
Branch Coverage:	65.92%
Branches in Coverage %:	Yes
Coverage Strength:	3.28 hits per line

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💛 - Coveralls

[hohwille]

@Paras14 thanks for your update. Now things are clean and almost perfect 👍
I left some final remarks easy to address but then we are finally merge.

[hohwille]

@Paras14 Perfect for merge now 👍