feat(js): Parse debug ids from scraped source files

[timfish]

I've been working on some bundler plugins that inject debug ids as per the TC39 proposal.

Since there's no cheap way to get debug ids from source files in the browser, this PR adds parsing of debug id from source files when they're scraped which can later be used to lookup the sourcemap.

The JavaScript SDKs can't rely on source files being publicly available and/or scraping working so we will still have to use polyfills and pass debug ids from the client. So this change doesn't improve things from the SDK perspective (no reduction in bundle or payload size), but I though symbolicator should probably still support this.

Let me know if this is worth adding and I'll try and add some tests!

[loewenheim]

Thank you very much for the contribution, I think this is a good idea and seems like a simple change. Tests would be appreciated!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 73.95%. Comparing base (5a85fd7) to head (614eecf).
Report is 158 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1534      +/-   ##
==========================================
- Coverage   76.09%   73.95%   -2.15%     
==========================================
  Files         101      104       +3     
  Lines       15262    15870     +608     
==========================================
+ Hits        11613    11736     +123     
- Misses       3649     4134     +485     

[loewenheim]

Do you have a test case demonstrating the improvement that you can add?

[timfish]

I will add a test, I've just not had a chance yet!

[timfish]

Test added!

It has a source file which isn't included in the artifact bundle which causes it to be scraped. Once scraped, the debug id parsed and then used to lookup the sourcemap from the bundle.

[loewenheim]

Very nice! Would you mind adding a changelog entry?