[AArch64][GlobalISel] Legalize wide s8/s16 vectors G_ADD/G_MUL/G_OR/...

Clamp the max number of elements of s8/s16 vectors when legalizing G_ADD,
G_SUB, G_MUL, G_AND, G_OR, G_XOR, in order to support some wide vectors.

Fixes https://github.com/llvm/llvm-project/issues/58156.

Differential Revision: https://reviews.llvm.org/D143517