[AArch64][GlobalISel] Widen G_SELECT before clamping it

This allows us to handle the s88 G_SELECTS:

https://godbolt.org/z/5s18M4erY

Weird types like this can result in weird merges.

Widening to s128 first and then clamping down avoids that situation.

Differential Revision: https://reviews.llvm.org/D107415