[llvm] Implemented MVT::changeElementType based on EVT::changeElementType (PR #206783)

[Simon Pilgrim via llvm-commits]

https://github.com/RKSimon commented:

There's some more case in X86ISelLowering.cpp with patterns like:
```
VT.isVector() ? VT.changeVectorElementType(MVT::f32) : MVT::f32;
```
which can be converted to
```
 VT.changeElementType(MVT::f32)
```

https://github.com/llvm/llvm-project/pull/206783