extensionUtils: Stop using RegExp for stack parsing

extensionUtils: Stop using RegExp for stack parsing

We currently use a regular expression to extract the exact file path
from a stack line. That RE is no longer accurate:

 - we assume a line number at the end, but at one point the column
   number was added as well
 - stacks from ES modules use file:// URIs instead of plain paths

Luckily that doesn't matter: We don't want to access any actual
files, so all we need is a path that can be traversed and that
contains the UUID.

We can get that with simple string manipulation, so avoid the regex
overhead.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2832>