Remove redundant top-level describe wrappers from @typespec/compiler tests

[timotheeguerin]

Follow-up to #11205, applying the same cleanup to the @typespec/compiler package.

Per CONTRIBUTING.md, a single describe(...) wrapping an entire test file is redundant (the file name already provides context). This PR removes those top-level wrappers and dedents the contents, using it() directly at the top level. Nested/sub-group describe() calls are left intact.

Scope

• 72 compiler test files unwrapped (single top-level describe, no top-level it/test).
• Excluded files still using the legacy test host and files with legitimate sub-group describes.
• Excluded 3 templates/ files (tsp init scaffolding, not compiler tests).

Notes

• Position-sensitive server tests (folding, hover, document-highlight, rename) required a template-literal-aware dedent so that multi-line source strings keep their exact indentation (and hardcoded line/column assertions stay valid).
• 7 files have minor prettier reflows (lines collapsing after dedent); no logic changes.

Validation

• All 4005 compiler tests pass.
• prettier and oxlint clean.

[pkg-pr-new]

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npm i https://pkg.pr.new/@typespec/compiler@11208

commit: 1fc7674

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