fix(developer): improve uploading of sourcemaps to sentry

Fixes #10720.

This makes three fixes:
* Uploads each sourcemap path separately to try and avoid the 413 error
  noted in the issue above.
* Starts from the parent folder, as it is possible that paths starting
  with .. may be ignored, as they were not being uploaded to sentry.
* Removes a number of unneeded test files and debug symbols, which
  should reduce the size of each release's debug data upload, and
  slightly speed up the build.