fix(debug): support multi-process debug attach and Jazelle runfiles layout

[harunaOseni]

Summary

Fixes breakpoint debugging in Jazelle/Bazel multi-process environments by:

• Multi-endpoint debug attachment: The extension now follows the full process chain (untar.js -> execute-command.js -> yarn -> jest) instead of attaching to the first endpoint and stopping. When a new endpoint appears, it resumes the current wrapper, detaches, and attaches to the new one. Last endpoint wins.
• Correct remote root path resolution: getDebugRemoteRoot now checks which runfiles layout exists on disk — standard Bazel (test_/test.runfiles/__main__) vs Jazelle (test.runfiles/__main__) — instead of always assuming the nested layout.

Problem

Three issues prevented breakpoint debugging from working in Jazelle environments:

1. Multi-endpoint debug attachment

The original extension attached to the first Debugger listening on endpoint and stopped looking. Jazelle/Bazel spawns a chain of wrapper Node processes, each emitting its own debug endpoint. The debugger was attaching to a wrapper (e.g. untar.js) instead of the actual Jest test runner.

2. Wrong remote root path

getDebugRemoteRoot was generating .../test_/test.runfiles/__main__ but Jazelle's actual layout is .../test.runfiles/__main__ (no test_/ prefix). Breakpoints couldn't bind because the debugger was mapping local files to a path that didn't exist at runtime.

3. Missing launch config for source maps

The "Attach to Bazel Test" launch config was missing sourceMaps: true, resolveSourceMapLocations, and .pnp.cjs in skipFiles. Without these, the debugger couldn't resolve babel-jest's source maps back to the original .ts files, and it was pausing on Yarn's PnP bootstrap instead of at breakpoints. (This is a launch.json change on the user side, not in this PR.)

Changes

• src/test-runner/run-tracker.ts: Replaced the single-attach debug flow with attachDebugger() — a single method that detaches any existing session and attaches to the new endpoint. Removed hasDebugSessionBeenInitiated flag (replaced by checking vscode.debug.activeDebugSession directly).
• src/language-tools/typescript.ts: getDebugRemoteRoot now uses fs.existsSync to check for the nested targetName_/ directory and includes it only if present.

Test plan

• Verified breakpoint debugging works in Jazelle/Bazel Jest tests (multi-process chain)
• Verified standard Bazel debug flow is unaffected (single endpoint, nested runfiles layout)