[lld-macho] Canonicalize personality pointers in EH frames

We already do this for personality pointers referenced from compact
unwind entries; this patch extends that behavior to personalities
referenced via EH frames as well.

This reduces the number of distinct personalities we need in the final
binary, and helps us avoid hitting the "too many personalities" error.

I renamed `UnwindInfoSection::prepareRelocations()` to simply `prepare`
since we now do some non-reloc-specific stuff within.

Fixes #58277.

Reviewed By: #lld-macho, oontvoo

Differential Revision: https://reviews.llvm.org/D135728

(cherry picked from commit 7b45dfc6)