Rewrite source paths in sourcemaps from being relative to the sourcemap
URL (eg. "../../src/path/to/file.js") to absolute URLs ("app:///src/path/to/file.js").
This ensures that the resolved source URLs, which result from joining
the sourcemap URL to the source path, remain consistent across releases.
This in turn improves issue grouping.

For a full explanation of how Sentry processes JavaScript crash
reports and determines the fingerprint used to group issues, see
https://gist.github.com/robertknight/cbdee9db50601c5244d9e483930c32ca.