Deterministic output

[robtfm]

fix OS-level shader caching by switching to IndexMap to maintain naga's deterministic output.

[Elabajaba]

Works for me (tested on bevy by dumping the shaders and comparing hashes/file contents with some local changes to bevyengine/bevy#11614 to dump all the shaders instead of overriding them every new compile, and by checking with a profiler that the drivers were no longer recompiling shaders every run).