JetBrains: store IntelliJ/PyCharm/Android Studio metadata under $IDE_HOME/.ide + migration

[quando632]

Feature idea

As an IntelliJ, PyCharm or Android Studio user, I want the IDE-specific metadata (.idea, *.properties, .vmoptions) to be stored outside of my workspace under $IDE_HOME/.ide/«ide»/«workspace» so that my workspace stays clean and independent of the IDE being used.

Additional context

Part of #2142. Builds on #2172 (getIdeMetadataPath()).

The three JetBrains-based IDEs share the superclass IdeaBasedIdeToolCommandlet, so most of the change can be solved once in the common super-class:

• vmoptions: switch the central write in IdeaBasedIdeToolCommandlet.runTool from the workspace to getIdeMetadataPath().
• *.properties env vars (IDEA_PROPERTIES, PYCHARM_PROPERTIES, STUDIO_PROPERTIES): point to getIdeMetadataPath().
• .idea (IntelliJ only): needs a spike first — IntelliJ expects .idea in the opened project root, so relocation likely requires a symlink or idea.config.path in idea.properties. To be clarified before implementation.
• Migration: move existing metadata of all workspaces to the new location (idempotent), registered in IdeMigrator.

IdeMigrator requires strictly ascending migration versions — coordinate the migration version with #2174 depending on merge order.

[quando632]

Scope split after code investigation: only the vmoptions are cleanly relocatable (written directly by code) and are handled in PR #2208. The .idea folder and the *.properties files are entangled with IntelliJ's project-root convention and the workspace-template-merge mechanism, so they are moved to a dedicated design spike: #2209.

So this issue is effectively resolved by #2208 (vmoptions) once merged; .idea + *.properties continue in #2209.