[llvm] [GlobalIsel] combine extract vector element (PR #91922)

[Thorsten Schütt via llvm-commits]

tschuett wrote:

>From the Gisel documentation:
```
Combiner

Replaces patterns of instructions with a better alternative. Typically, this means improving run time performance by replacing instructions with faster alternatives but Combiners can also focus on code size or other metrics.
```

https://github.com/llvm/llvm-project/pull/91922