[llvm] [VectorCombine] Prevent extract/ins rewrite to GEP (PR #150216)

[Nathan Gauër via llvm-commits]

Keenuts wrote:

> Is there no TTI hook we can use?

Would it be OK to move forward with a target-specific switch?
I could also add a new bit like "disableVectorElementAccessUsingGEP" which would allow to prevent this on a target-by-target basis until the pattern is officially disallowed? (if it is one day)

https://github.com/llvm/llvm-project/pull/150216