[Windows] Improve warning for path casing.

[AThousandShips]

Expands the warning for case mismatch for paths, restricted to paths in res:// and user:// and relative paths, partially to avoid false positives I ran into with fonts (it seems that the system font lookup gives you WINDOWS regardless of the actual spelling on your computer), and my reasoning is that absolute paths are unlikely to be portable anyway, nor do I even think they are advisable in a project.

Related to #52231 but not a complete solution for that, but probably relevant for the implementation. But I think a more helpful check here will still be needed for dynamic cases even if hardcoded paths in scripts and scenes should be fixed some way.

Edit:
There is a now unused fix for casing in os_windows but I'm leaving that there for now unless told otherwise.

[akien-mga]

Poke @bruvzg

[AThousandShips]

Gonna just test this on my own build for completeness today unless you did so @bruvzg, haven't rested this for the better part of a year so wanna make sure

[bruvzg]

Gonna just test this on my own build for completeness today unless you did so @bruvzg, haven't rested this for the better part of a year so wanna make sure

For the reference, I have only looked at the code, and it looks fine to me, have not tested it on Windows.

[AThousandShips]

Had it in my working branch and it correctly reports path casing errors in full paths like res://asteroids/Asteroid.gd for the proper res://Asteroids/Asteroid.gd, didn't check the user:// path but it's equivalent

[akien-mga]

Thanks!

[AThousandShips]

Thank you!