Unified UI setting for toolchains

[G-Ork]

I redesigned the Maven user settings and add the sections Global & User. For booth there are now settings & toolchains options.

• Added default path hints for global settings and global toolchains. They are only rendered for external maven installations. Don't forget to apply changes to see them.
• Unify settings override through goals field. All four settings could be put into the goal in short form (-gt. -gs, -t, -s).
• Throw exception during launch if path to a settings file is invalid.
• Provide unit-tests for maven launcher for all four settings
• Fix a bug in settings validation. Parser problems are not copied to result if parser do not crash. All well formed xml-files are treated as valid.

[github-actions]

Test Results

0 files   -   214  0 suites   - 214   0s ⏱️ - 22m 41s
0 tests  -   665  0 ✅  -   655  0 💤  - 10  0 ❌ ±0 
0 runs   - 1 330  0 ✅  - 1 308  0 💤  - 22  0 ❌ ±0 

Results for commit 195f29e. ± Comparison against base commit a680216.

♻️ This comment has been updated with latest results.

[akurtakov]

Is there interest if finishing this one?

[laeubi]

@G-Ork can you pleas squash all commits and rebase on main?

[G-Ork]

I'll do my best to squeeze the squash it into this weekend.