Skip more work when creating LSP watch globs

[jakebailey]

I realized after the fact that getDirectoryToWatchFailedLookupLocation doesn't really care about the actual contents of the path, just how the parts split apart and where node_modules is. This means that passing in /foo/node_modules/bar/index.js and /foo/node_modules/bar/blah.js will return identical results.

Prevent the expensive call to getDirectoryToWatchFailedLookupLocation by only doing it once per dirname.

In my testing, this halves the amount of time spent mapping paths to globs. From:

Info 9    [11:42:17.604] createGlobMapper took 86.409653ms to create 3 globs for 31663 failed lookups
Info 10   [11:42:17.739] failed lookup watches updated watcher-1:
	/home/jabaile/work/node_modules/**/*.{js,jsx,mjs,cjs,ts,tsx,mts,cts,json}
	/home/jabaile/work/vscode/node_modules/**/*.{js,jsx,mjs,cjs,ts,tsx,mts,cts,json}
	/home/jabaile/work/vscode/src/**/*.{js,jsx,mjs,cjs,ts,tsx,mts,cts,json}

To:

Info 9    [11:43:02.173] createGlobMapper took 37.743599ms to create 3 globs for 31663 failed lookups
Info 10   [11:43:02.409] failed lookup watches updated watcher-1:
	/home/jabaile/work/node_modules/**/*.{js,jsx,mjs,cjs,ts,tsx,mts,cts,json}
	/home/jabaile/work/vscode/node_modules/**/*.{js,jsx,mjs,cjs,ts,tsx,mts,cts,json}
	/home/jabaile/work/vscode/src/**/*.{js,jsx,mjs,cjs,ts,tsx,mts,cts,json}

The halving also carries over to #995.

[Copilot]

Pull Request Overview

This PR improves performance by reducing redundant calls to getDirectoryToWatchFailedLookupLocation when creating LSP watch globs.

• Introduces caching of directory paths using a Set from the core package.
• Skips duplicate processing for files within the same directory to halve the work required for lookup globs.

Comments suppressed due to low confidence (1)

internal/project/watch.go:105

• [nitpick] Consider renaming 'seenDirs' to 'processedDirectories' for improved clarity on its purpose.

var seenDirs core.Set[string]

[jakebailey]

Test failure is an ATA flake. Looking into that right now.