Add and use a `naga_oil` macro to abstract over material texture sampling shader code

> Yeah, I'd love a macro in `naga_oil`. We could do a lot with macros, not just [meshlets/normal code paths]. For example, we could abstract over bindless/non-bindless declarations.

_Originally posted by @pcwalton in https://github.com/bevyengine/bevy/issues/16644#issuecomment-2521267614_

Start by reading the naga_oil macro entry point and tracing the material texture sampling shader code referenced in the issue. Map how bindless and non-bindless declarations, including the meshlets and normal code paths, would use the macro; done means the macro exists and those sampling paths use it.

Written by the indexing model from the issue text.