Fixes#18029.
There are ways to load assemblies that the search hook has no way of intercepting,
and handling itself. Such as loading from a byte[] in C# code.
We now handle these cases with a fallback assembly_load_hook,
to avoid crashes when this is indeed done.
- Setup runtime main args during initialization. This must be done manually by embedders who do not call mono_runtime_run_main. Fixes NullReferenceException in System.Environment.
- Continue to search the assembly in the rest of the search locations if loading it from one of them failed.
- Bundle with mscorlib.dll to avoid compatibilities issues
- Add build option 'mono_assemblies_output_dir' to specify the output directory where the assemblies will be copied to. '#bin' by default.
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.
