[LoongArch] Override LoongArchTargetLowering::getExtendForAtomicCmpSwapArg (#83656)

This patch aims to solve Firefox issue:
https://bugzilla.mozilla.org/show_bug.cgi?id=1882301

Similar to 616289ed. Currently LoongArch uses an ll.[wd]/sc.[wd]
loop for ATOMIC_CMP_XCHG. Because the comparison in the loop is
full-width (i.e. the `bne` instruction), we must sign extend the input
comparsion argument.

Note that LoongArch ISA manual V1.1 has introduced compare-and-swap
instructions. We would change the implementation (return `ANY_EXTEND`)
when we support them.

(cherry picked from commit 5f058aa2)