test: data-driven validation tests

[lars-reimann]

Closes partially #543.
Closes partially #433.

Summary of Changes

• Port the data-driven framework for validation tests from the old Xtext implementation to Langium.
• Document how to write validation tests.

[codecov]

Codecov Report

Merging #556 (7d24e8d) into main (befa503) will decrease coverage by 0.04%.
The diff coverage is 99.24%.

@@            Coverage Diff             @@
##             main     #556      +/-   ##
==========================================
- Coverage   99.55%   99.52%   -0.04%     
==========================================
  Files           5        6       +1     
  Lines        1135     1256     +121     
  Branches      238      276      +38     
==========================================
+ Hits         1130     1250     +120     
- Misses          5        6       +1     

Files Changed	Coverage Δ
src/language/validation/nameConvention.ts	99.19% <99.19%> (ø)
src/language/constant/fileExtensions.ts	98.61% <100.00%> (+0.10%)	⬆️
src/language/validation/safe-ds-validator.ts	100.00% <100.00%> (ø)

[github-actions]

🦙 MegaLinter status: ✅ SUCCESS

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
✅ MARKDOWN	markdown-link-check	1		0	0.34s
✅ REPOSITORY	git_diff	yes		no	0.05s
✅ TYPESCRIPT	eslint	14	0	0	4.85s
✅ TYPESCRIPT	prettier	14	0	0	1.21s

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[lars-reimann]

🎉 This PR is included in version 0.2.0 🎉

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