Split gz.ts properly into node and browser variants

[mstange]

I noticed that webpack was still including the gz worker in the generated symbolicator-cli bundle. And esbuild was even putting it in a separate file. But we don't need the gz worker in the symbolicator-cli bundle; symbolicator-cli targets node so we really just want to run the node version of gz.ts.

This PR makes the "node" version the default behaviour of gz.ts, and then adds a browser override via the package.json "browser" mapping to use the worker version.

In our tests we want to use the worker version though, because we want to test what happens in a browser environment. So we use a custom jest-resolver.js. I tried to use browser-resolve (as suggested in the Jest docs) in it but it ended up resolving some ESM dependencies like valibot to their mjs variant instead of their CJS variant and broke the tests, so I kept a manual implementation instead. I didn't dig very deep.

With this change, the symbolicator-cli bundle no longer contains the gz worker code.

[codecov]

Codecov Report

❌ Patch coverage is 57.57576% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 85.67%. Comparing base (98b5328) to head (3278553).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/utils/gz.ts	0.00%	12 Missing ⚠️
src/utils/gz.browser.ts	90.47%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5764      +/-   ##
==========================================
- Coverage   85.69%   85.67%   -0.02%     
==========================================
  Files         316      317       +1     
  Lines       31141    31145       +4     
  Branches     8582     8584       +2     
==========================================
- Hits        26686    26684       -2     
- Misses       4025     4031       +6     
  Partials      430      430              

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