Summary:This adds support for source maps that can be used for “random access modules” / “unbundles”
- source maps contain an extra custom field: `x_facebook_offsets`
- this field maps module IDs to line offsets
- the source map is built as if all files were concatenated
Decoding/symbolication works as follows:
- when decoding a stack trace, and a stack frame comes from a filename that contains only numbers and ends with `.js`, look up the additionally needed line offset in the offset map and add it to the original line of the stack frame.
- consume the source map as usual
Reviewed By: martinbigio
Differential Revision: D3072426
fb-gh-sync-id: 827e6dc13b1959f02903baafa7f9e4fc2e0d4bb9
shipit-source-id: 827e6dc13b1959f02903baafa7f9e4fc2e0d4bb9
