[lldb-dap] Experimenting with async in DAP tests.

This is not fully tested yet, but the basic approach is to remove the background thread that can cause races in the tests.

Instead, I am using an asyncio event loop to read packets, and the tests can await on the loop to process packets as needed.

With further refactoring we should be able to push the async operations further up the stack into the test cases themselves.

Author: ashgti

lldb/packages/Python/lldbsuite/test/dotest.py

@@ -300,7 +300,8 @@ def parseOptionsAndInitTestdirs():
             configuration.libcxx_include_target_dir = args.libcxx_include_target_dir
             configuration.libcxx_library_dir = args.libcxx_library_dir
 
-    configuration.cmake_build_type = args.cmake_build_type.lower()
+    if args.cmake_build_type:
+        configuration.cmake_build_type = args.cmake_build_type.lower()
 
     if args.channels:
         lldbtest_config.channels = args.channels