[lld][ELF][AArch64] Handle R_AARCH64_PLT32 relocation

This is the followup to D77647 which implements handling for the new
R_AARCH64_PLT32 relocation type in lld. This relocation would benefit the
PIC-friendly vtables feature described in D72959.

Differential Revision: https://reviews.llvm.org/D81184