[llvm] [VectorCombine] foldShuffleToIdentity - handle bitcasts with equal element counts (PR #97731)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

llvm-reduce came up with:
```ll
define void @_ZN3hwy7N_SSSE325TestLoadStoreInterleaved3clIiNS0_4SimdIiLm4ELi0EEEEEvT_T0_() {
entry:
  %shuffle.i.i = shufflevector <2 x i64> zeroinitializer, <2 x i64> zeroinitializer, <2 x i32> <i32 1, i32 3>
  %0 = bitcast <4 x i32> zeroinitializer to <4 x float>
  %1 = bitcast <2 x i64> %shuffle.i.i to <4 x float>
  %shufp.i196 = shufflevector <4 x float> %0, <4 x float> %1, <4 x i32> <i32 2, i32 1, i32 4, i32 7>
  store <4 x float> %shufp.i196, ptr null, align 16
  ret void
}
```

https://github.com/llvm/llvm-project/pull/97731