refactor(ts-plugin): split go-to-definition e2e tests into per-behavior cases

[mizdra]

Summary

Refactor packages/ts-plugin/e2e-test/feature/go-to-definition.test.ts so that each test block owns a minimal fixture and asserts a single behavior, organized by the .d.ts/mapping pattern under test. The previous structure shared one large fixture (5 files, 8+ tokens) across 17 cases inside a single test.each, which made it brittle to add new behaviors.

This is the first PR of a multi-PR series. Subsequent PRs will apply the same approach to the other e2e-test/ files (find-all-references, rename-symbol, completion, etc.).

What's new

• packages/ts-plugin/e2e-test/test-util/fixture.ts: adds
  • setupFixture(files) — mirrors createIFF's shape; callers pass files directly (including tsconfig.json), so each test can place its config wherever it likes.
  • getLoc(file, search, index?) — 1-based line/offset of the first character of search in file. Throws if search is ambiguous and index is omitted.
  • getRange(file, search, index?) — { start, end } range with end exclusive (matches tsserver's convention).
• packages/ts-plugin/test/builder.ts (new): code-fragment builders for fixture files
  • buildTSConfigJSON({ compilerOptions?, cmkOptions? }) — defaults cmkOptions.enabled to true.
  • buildStylesImport(specifier, { namedExports }) — builds default / namespace styles import statements at call sites.
• packages/ts-plugin/e2e-test/feature/go-to-definition.test.ts: rewritten as 14 behavior-focused tests, each with its own minimal fixture, organized into 4 describe blocks. Each fixture uses contiguous token / filename numbering (e.g. a.module.css + b.module.css, .a-1, b_1) so it only references the files and tokens the test actually needs.

Test structure

Each describe corresponds to a distinct .d.ts/mapping pattern produced by dts-generator.ts:

namedExports: $namedExports
├── jumps to the top of a CSS module file (5 tests)
│   ├── from the styles binding in the import statement
│   ├── from the import specifier string
│   ├── from the @import specifier string
│   ├── from the @value ... from specifier string
│   └── from inside the @import url(...) parenthesis
├── jumps to a local token declaration (3 tests)
│   ├── from styles.<token> access
│   ├── from styles[<kebab-case token>] access
│   └── returns all declarations when the same class is declared multiple times
├── transitively resolves a re-export to its source declaration (3 tests)
│   ├── class re-exported via @import
│   ├── value re-exported via @value ... from
│   └── aliased value re-exported via @value ... from
└── jumps from a CSS-side @value ... from binding to its source declaration (3 tests)
    ├── from the import binding
    ├── from the alias name in \`name as alias\`
    └── from the source name in \`name as alias\`

Total: 14 tests × 2 variants (namedExports: false / true) = 28 tests.

Per-syntax parser coverage (e.g. .foo, @value foo: red;, @keyframes foo) lives in dts-generator.test.ts; here we only cover one representative for each .d.ts/mapping pattern.

Test plan

• vp test --project e2e packages/ts-plugin/e2e-test/feature/go-to-definition.test.ts — 28 passed
• vp test --project e2e (full e2e suite) — no regressions
• vp check (format + lint + type) — pass

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