[lldb-dap] Change the launch sequence (#138219) (reland)
This PR changes how we treat the launch sequence in lldb-dap.
- Send the initialized event after we finish handling the initialize
request, rather than after we finish attaching or launching.
- Delay handling the launch and attach request until we have handled
the configurationDone request. The latter is now largely a NO-OP and
only exists to signal lldb-dap that it can handle the launch and
attach requests.
- Delay handling the initial threads requests until we have handled
the launch or attach request.
- Make all attaching and launching synchronous, including when we have
attach or launch commands. This removes the need to synchronize
between the request and event thread.
Background:
https://discourse.llvm.org/t/reliability-of-the-lldb-dap-tests/86125
