I also removed a debug assertion that wasn't true when a debug session
was restarting through a request, because there wasn't a booting task
Zed needed to run before the session.

I renamed SessionState::Building to SessionState::Booting as well,
because building implies that we're building code while booting the
session covers more cases and is more accurate.

Release Notes:

- debugger: Filter out more invalid debug configurations from the debug
picker

Co-authored-by: Remco Smits <djsmits12@gmail.com>