[llvm] [VectorCombine] Try to scalarize vector loads feeding bitcast instructions. (PR #164682)

[Simon Pilgrim via llvm-commits]

https://github.com/RKSimon commented:

I'd be much easier with the patch if it was merely:
```
m_BitCast(m_OneUse(m_Load()))
```
I'm not clear on the need for iterating across users etc.

https://github.com/llvm/llvm-project/pull/164682