coredump: Enable understanding of threads in scripts

Update zephyr gdb-server scripts to understand threads.

Parse the kernel_thread_info out of the elf file to be used
for finding offsets to data from _kernel structs or from
individual threads.

Update log_parser to understand latest format change, which
allows for the presence of a new section, threads metadata.

Update gdbstub to respond to various packets to describe
the threads present in a dump, and allow switching to
thread context of each thread.

Signed-off-by: Mark Holden <mholden@meta.com>