Recognize `addressing_bits` kv in stop reply packet

If a remote stub provides the addressing_bits kv pair in
the stop reply packet, update the Process address masks with
that value as it possibly changes during the process runtime.
This is an unusual situation, most likely a JTAG remote stub
and some very early startup code that is setting up the page
tables.  Nearly all debug sessions will have a single address
mask that cannot change during the lifetime of a Process.

Differential Revision: https://reviews.llvm.org/D149803
rdar://61900565