feat: narrow outFiles to workspace dependencies in npm/yarn monorepos

[Aparajith (Aparajith24)]

In an npm/yarn workspaces monorepo, outFiles was previously left to fall back to scanning the entire opened folder for sourcemaps. This happened because the widen-only logic in guessOutFiles only kicks in when the debugged program lives outside the opened workspace folder, but in a monorepo, the folder VS Code has open typically is the repo root, so the program is always "inside" it and the widen logic never narrows anything. The result: debugging one package in a large monorepo scanned every other unrelated package's compiled output too, making it slow to hit breakpoints.

This adds a narrower path: when the opened workspace folder itself has a "workspaces" field in its "package.json" (npm/yarn workspaces), we:

1. Find the specific package being debugged (nearest package.json walking up from the entry file).
2. Read the workspace's package list from the workspaces glob patterns (e.g. packages/*).
3. Walk that package's dependencies/devDependencies/peerDependencies to find which of them are other packages in the same workspace*.
4. Set outFiles to just the debugged package plus those workspace-local dependencies, instead of the whole repo.

This only applies when outFiles isn't already set by the user (same guard the existing widen-only logic uses), so anyone with a manually configured outFiles is unaffected. Projects without a workspaces field are also completely unaffected, this is additive, not a change to existing behavior.

Closes #1730

[Aparajith (Aparajith24)]

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