Add **/node_modules to file_scan_exclusions

[tekacs]

For new users on my team, the first thing that we have to change to get viable search performance is adding "**/node_modules" to file_scan_exclusions.

Apologies if this is the wrong way to solve this problem, but search is interminably slow and painful without this change, so I thought I'd try PR-ing this addition to see if there's appetite for including it by default!

Release Notes:

• Improved the default file_scan_exclusions by including "**/node_modules", to improve search performance by default.

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[tekacs]

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[SomeoneToIgnore]

Thank you, but this does not look like a good solution indeed:

• we have a project search feature, that allows to look search in ignored, but not excluded, files — merging this PR will break such searches
• file finder is also requested to match ignored files, and that matching has to be fast, hence indexed somehow — excluded files are not indexed

Both features were used/required with node_modules specifically, based on the feedback.

What's more interesting, current implementation of Zed does not traverse ignored roots unless those are expanded — so interesting to know the details on how the performance degrades.

It would also be interesting to get things profiled and see what's slow actually.

If all above sounds too hard, the only good bandage aid on top I can think of is #7195 — then you would be able to store the exclusion in the repo, propagating it to every teammate automatically.