feat(debug-files): add --il2cpp-mapping for Unity IL2CPP line mappings

[BYK]

Stacked on #1163 (embedded Portable PDB extraction). Review that first; GitHub will retarget this PR's base to main automatically once #1163 merges. The diff shown here is only this PR's changes.

What

Adds sentry debug-files upload --il2cpp-mapping: for each prepared debug file it computes a Unity IL2CPP C++→C# line mapping (from the file's primary debug-info object) and uploads it as a separate il2cpp DIF carrying the object's debug id — faithful to legacy sentry-cli's create_il2cpp_mappings.

Consumes the new WASM API from @sentry/symbolic@13.7.0 (getsentry/symbolic#1005):

• top-level il2cppLineMapping(object, provider)
• SourceBundleWriter.collectIl2cppSources (present since 13.5.0)

Behavior (matches legacy)

• The generated C++ source files an object references are read from disk via a provider; IL2CPP //<source_info:File.cs:line> markers are parsed from them. Objects that yield an empty mapping are skipped.
• The mapping DIF is named <name>.il2cpp and carries the source file's debug id.
• When combined with --include-sources, the per-file source bundle also collects the referenced C# source files (collectIl2cppSources) — otherwise the source bundle is unchanged.
• Missing/unreadable sources and mapping failures are swallowed (debug-logged), never aborting the upload.
• --symbol-maps (BCSymbolMap resolution) remains the only deferred legacy upload option.

Implementation

• src/lib/dif/index.ts: createIl2cppLineMapping(data, readSource) + a collectIl2cppSources option on createSourceBundle().
• src/commands/debug-files/upload.ts: --il2cpp-mapping flag; extracted a shared readSourceFile disk-reader used by both the source bundle and the IL2CPP provider.

Tests

• test/lib/dif/il2cpp.test.ts — createIl2cppLineMapping (mapping JSON, provider-null → null, no-markers → null) and createSourceBundle collectIl2cppSources (C# included only when enabled, verified by unzipping the bundle).
• test/commands/debug-files/upload.test.ts — --il2cpp-mapping queues the .il2cpp DIF, absent without the flag, and is threaded through to uploadDebugFiles.

All text fixtures (Breakpad FILE records + synthetic C++/C#), no binaries.

Verified locally: typecheck, lint, test (358 debug-files/dif/scan tests), check:deps, check:fragments all green.

[github-actions]

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[github-actions]

Codecov Results 📊

❌ Patch coverage is 76.92%. Project has 5140 uncovered lines.
✅ Project coverage is 81.5%. Comparing base (base) to head (head).

Files with missing lines (2)

File	Patch %	Lines
src/commands/debug-files/upload.ts	64.29%	⚠️ 5 Missing and 1 partials
src/lib/dif/index.ts	91.67%	⚠️ 1 Missing and 1 partials

Coverage diff

@@            Coverage Diff             @@
##          main       #PR       +/-##
==========================================
+ Coverage    81.50%    81.50%        —%
==========================================
  Files          399       397        -2
  Lines        27744     27777       +33
  Branches     18025     18051       +26
==========================================
+ Hits         22609     22637       +28
- Misses        5135      5140        +5
- Partials      1859      1864        +5

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[BYK]

Superseded by #1165. GitHub auto-closed this PR when its base branch (byk/feat/debug-files-embedded-ppdb, #1163) was deleted on merge; the same commit, rebased onto main, continues in #1165.