[mach-o] add support for arm64 compact unwind info

Tim previously added generic compact unwind processing and x86_64 support.
This patch adds arm64 support.
[mach-o] Fix TrieEdge leak

In PR21682 Jean-Daliel Dupas found a leak in the trie builder and suggested
a fix was to use a list instead of SmallVector so that the list elements
could be allocated in the BumpPtrAllocator.