Add test case for remapping of absolute paths in panic messages

[brson]

In #1594 we added a fetature to remap absolute file paths in panic messages (and debuginfo) to relative paths, for reproducibility.

That issue did not land any tests - the feature is complicated to test, but we did discuss methods for testing it.

Also in that thread it was mentioned that we probably screwed up on windows specifically, because the feature as implemented does not work with spaces in paths, and windows home directories commonly contain spaces.

Let's write a test and fix the implementation on windows.