Updated all code necessary to run on wgpu 0.15. For now the new
view_formats aren't really used and just contain the same format as the
texture. The new instance descriptor uses the FXC compiler for Windows
and all others. For all others it shouldn't matter as it is Windows
only. For Windows the possibility of using the DXC compiler should be
explored as it seems to be a better alternative to FXC
(https://docs.rs/wgpu-types/0.15.1/wgpu_types/enum.Dx12Compiler.html#variants).

In wgpu 0.15 global let statements in wgsl shader code was removed in
favor of global const statements. This commit addresses those changes.

The last commit removed the MeshMetadata shader code from a shader which
was used as a header and broke other code. This commit readds it to the
header shader and removes it from the actual offending shader with a
double definition.