Fix watch diagnostics when global declaration is removed

[John Favret (johnfav03)]

Fixes #4838

When a script file stopped affecting the global scope, the incremental affected-files calculation used its new affectsGlobalScope value. If a global declaration was commented out or removed, the file no longer affected global scope, so only that file was rechecked. This meant that other files using that variable would retain stale semantic diagnostics and that watch mode would fail to report an error.

[Copilot]

Pull request overview

Fixes stale watch diagnostics when a changed script stops contributing to the global scope.

Changes:

• Detects loss of global-scope impact and marks all relevant files changed.
• Adds watch-mode regression coverage for removing and restoring a global declaration.
• Adds the expected watch baseline.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
internal/execute/incremental/programtosnapshot.go	Invalidates files after global-scope loss.
internal/execute/tsctests/tscwatch_test.go	Adds the watch regression scenario.
testdata/baselines/reference/tscWatch/commandLineWatch/watch-detects-error-across-global-script-files-when-global-decl-removed.js	Records expected diagnostics and rebuilds.

[Jake Bailey (jakebailey)]

If it's not too much to ask, do you mind splitting this PR into two commits, where you add the test and baseline into the first commit, then the second commit is the fix with the baseline update that shows that it worked? Hard to tell for sure just from a one commit.

[John Favret (johnfav03)]

Just split the test and the fix into two commits; with just the test, a clean build should report TS2304: Cannot find name 'a' whereas the incremental watch incorrectly reports 0 errors.