Fix a problem exposed by #166483 using AV classes in more places.
`isVectorRegister` only accepts registers of VGPR or AGPR classes.
`hasVectorRegisters` additionally accepts the combined AV classes.

Fixes: #168761

Fixes another verifier error after introducing AV registers.
Also fixes not clearing the subregister index if there was
one.

Create utility mechanism for finding wave size dependent opcodes used to
manipulate exec/lane masks.

These cannot accept high registers.

This patch replaces SmallSet<T *, N> with SmallPtrSet<T *, N>.  Note
that SmallSet.h "redirects" SmallSet to SmallPtrSet for pointer
element types:

  template <typename PointeeType, unsigned N>
class SmallSet<PointeeType*, N> : public SmallPtrSet<PointeeType*, N>
{};

We only have 140 instances that rely on this "redirection", with the
vast majority of them under llvm/. Since relying on the redirection
doesn't improve readability, this patch replaces SmallSet with
SmallPtrSet for pointer element types.

When true16 is enabled, isel start to emit sgpr_lo16 register when a
trunc/sext i16/i32 is generated, or a salu32 is used by vgpr16 or vice
versa. And this causes a problem as sgpr_lo16 is not fully supported in
the pipeline.

True16 mode works fine in -O3 mode since folding pass remove sgpr_lo16
from the pipeline. However it hit a problem in -O0 mode as folding pass
is skipped.

This patch did:
1. stop emitting sgpr_lo16 from isel
2. update codegen pattern to split uniformed/divergent pattern for
i16/i32 conversion
3. update fix-sgpr-copy pass to address legalization requirement in
true16 mode, update fix-sgpr-copies-f16-true16.mir
test to include all possible combinations

This patch is tested with cts and downstream repo with -O0 testing