To help users writing good cross-platform code, Godot's
`FileAccessWindows:open()` will issue a warning on case mismatch, which
happens here with capitalized extensions given by `PATHEXT` compared to
actual file extensions which are lowercase 99% of the time.
Fixes#25368.
- Now there is only one solution that contains both GodotSharp and GodotSharpEditor project. Previously we had one solution for each project
- GodotSharpEditor reference GodotShatp with a 'ProjectReference'. Previously it was a 'Reference' to the assembly
- This also simplifies the command line option to generate this solution: 'godot --generate-cs-api <OutputDir>'
This allows more consistency in the manner we include core headers,
where previously there would be a mix of absolute, relative and
include path-dependent includes.
Using `misc/scripts/fix_headers.py` on all Godot files.
Some missing header guards were added, and the header inclusion order
was fixed in the Bullet module.
