Debugger: Move command flags to debugger command

Also, remove the need to mark GDB Python commands, detect the
need to use MI on the presence of non-Pythonic letters in
the command (space and hyphen).

Plan is to reuse even more almost shared code between engines.

Change-Id: I4e00debb07f2482637930675a28f464666b59553
Reviewed-by: hjk <hjk@qt.io>

src/plugins/debugger/lldb/lldbengine.cpp

@@ -414,7 +414,7 @@ void LldbEngine::setupInferior()
         }
     };
 
-    cmd2.flags = LldbEngine::Silent;
+    cmd2.flags = Silent;
     runCommand(cmd2);
 }