Handle errors in Metro by showing a code frame

Summary:
Right now the code frame and stack trace for metro errors are useless. This diff improved these errors by showing the metro code frame for the source of the issue, and stripping the stack trace.

Ideally we could show the metro stack trace as well, but since stack traces are tightly coupled to symbolication (and metro source code does not need symbolicated, nor could it be), this is an acceptable incremental improvement.

Arguably, even showing the code frame is inappropriate and we should show a generic crash screen with reload and report buttons.

Changelog: [Internal]

Reviewed By: cpojer

Differential Revision: D20057353

fbshipit-source-id: 5e999cea14c1cbd2f69737e3992a3e8d159fdf89