Remove NativeLibraryLoader

[smoogipoo]

No description provided.

[smoogipoo]

I've tested this on macOS (the only affected platforms, we don't use GL on macOS/iOS) in combination with ppy/veldrid-spirv#12 (with a fixed package reference), and I think this is good to go now.

[smoogipoo]

Benchmarks (git clean -xdf && dotnet build osu-framework.Desktop.slnf):

Run	master	remove-nll
1	7.58	8.34
2	6.77	6.36
3	8.84	6.25
4	7.91	7.41
5	6.59	6.03
6	7.65	7.47
7	6.43	6.97
8	8.21	6.86
9	7.29	7.65
10	6.64	6.22
Mean	7.391	6.956
Median	7.435	6.915
Std. Dev	0.7935496904	0.7549569524

GenerateDepsFile (top-10 most expensive tasks) goes from 3.7s to 2.6s