[LLDB] Support AArch64 PAC elf-core register read

[omjavaid]

Summary

This adds support for reading AArch64 Pointer Authentication regset
from elf-core file. Also includes a test-case for the same. Furthermore
there is also a slight adjustment of RegisterContextPOSIXCore_arm64
members and constructor.

[DavidSpickett]

lldb/source/Plugins/Process/elf-core/RegisterContextPOSIXCore_arm64.cpp

32

How is the sizeof() calculated here? Is it the size of the masks themselves, or a header block. (SVE above is clearly a header of some kind)

lldb/test/API/functionalities/postmortem/elf-core/TestLinuxCore.py

451

Do you need anything special to generate the core file? Might be worth noting in the commit message.

Though I guess you can just compile a hello world on a Linux system with PAC.

453

values = {
  "data_mask": "...",
  ...
}

(or dict(data_mask="..."))

[labath]

Seems reasonable to me. I'm happy if @DavidSpickett is.