[LegalizeTypes][AArch64] Use scalar_to_vector to eliminate bitcast

```
Legalize t3: v2i16 = bitcast i32
with   (v2i16 extract_subvector (v4i16 bitcast (v2i32 scalar_to_vector (i32 in))), 0)
```
Fix https://github.com/llvm/llvm-project/issues/61638

NOTE: Don't touch getPreferredVectorAction like X86 as this will touch
too many test cases.

Reviewed By: dmgreen, paulwalker-arm, efriedma
Differential Revision: https://reviews.llvm.org/D147678