Rename the function to reflect its correct behavior and to be consistent
with `Module::getOrInsertFunction`. This is also in preparation of
adding a new `Intrinsic::getDeclaration` that will have behavior similar
to `Module::getFunction` (i.e, just lookup, no creation).

Generated automatically with:
$ clang-tidy -fix -checks=-*,llvm-qualified-auto $(find
lib/Target/AMDGPU/ -type f)

The image intrinsic optimizer pass was neglecting to check any arguments
of the load intrinsic after the VAddr arguments. For example multiple
loads from different resources should not have been combined but were,
because the pass was not checking the resource argument.

Implement a new pass to combine multiple image_load_2dmsaa and
2darraymsaa intrinsic calls into a single image_msaa_load if:

- they refer to the same vaddr except for sample_id,
- they use a constant sample_id and they fall into the same group,
- they have the same dmask and the number of instructions and the
  number of vaddr/vdata dword transfers is reduced by the combine

This should be valid on all GFX11 but a hardware bug renders it
unworkable on GFX11.0.* so it is only enabled for GFX11.5.

Based on a patch by Rodrigo Dominguez!