This fixes a regression introduced in
https://github.com/zed-industries/zed/pull/2560, where panic reports did
not include backtraces. The problem was that in that PR, I assumed we
could retrieve file paths for symbols in our backtraces. But actually,
that functionality only works when the app is built locally, and a
`.dSYM` file can be magically found by the OS. We don't ship those dSYM
files with Zed, so panic symbols do not have file paths available.

Panic backtraces will still be more useful and less noisy than before
though: we will strip out frames for which we don't have symbol names,
and remove leading panic-handling stack frames from the backtraces.

Release Notes:

- N/A