[Transform] Rewrite LowerSwitch using APInt

This rewrite fixes https://github.com/llvm/llvm-project/issues/59316.

Previously LowerSwitch uses int64_t, which will crash on case branches using integers with more than 64 bits.
Using APInt fixes this problem. This patch also includes a test

Reviewed By: RKSimon

Differential Revision: https://reviews.llvm.org/D140747