Add thread exited event

Reports a thread exit according to the DAP spec:
https://microsoft.github.io/debug-adapter-protocol/specification#Events_Thread

This patch requires the ThreadExitedEvent to be checked in,
in order to work. That patch is found here https://sourceware.org/pipermail/gdb-patches/2023-June/200071.html

Formatted correctly using black

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30474

Approved-By: Tom Tromey <tom@tromey.com>
1 file changed