[lldb] [server] Support for multiprocess extension

Add a minimal support for the multiprocess extension in lldb-server.
The server indicates support for it via qSupported, and accepts
thread-ids containing a PID.  However, it still does not support
debugging more than one inferior, so any other PID value results
in an error.

Differential Revision: https://reviews.llvm.org/D98482

GitOrigin-RevId: 6c1a8039de4646f6efbb3ba404d5bee5d631be67
11 files changed