Debugger: Re-organize dock widget persisting

Looks like the mainwindow cannot be convinced to handle multiple
sets of dockwidgets.

So switch back to a single set containing everything and keep
track of non-default visibility in the perspectives, and persist
these sets.

The following pass:

1.

 Start Creator with new settings
 Goto Debug Mode
 Move Break dock widget to right, switch on Global log widget
 Leave Creator
 Start Creator
 Goto Debug Mode
 Check: Debugger Selected, Break on right, Global log visible

2.

 Start Creator with new settings
 Goto Debug Mode
 Move Break dock widget to right, switch on Global log widget
 Switch to QmlProfiler sub-perspective
 Leave Creator
 Start Creator
 Goto Debug Mode
 Check QmlProfiler selected
 Switch to Debugger sub-perspective
 Check: Debugger Selected, Break on right, Global log visible

3.

 Start Creator with new settings
 Use any C++ test project
 Start debugging / stop at main()  (F10)
 Wait for stop
 Switch to Edit mode
 Switch back to Debug mode
 Check: Only "running" debugger dock widget layout present
  (not the normal + preset at the same time)
 Quit Qt Creator while this debugger is running
 Check: Shuts down without crash

4.
 Use any C++ test project
 Start debugging
 Switch to Debugger Preset perspective
 Start a second debugger
 Kill either instance
 Check: Application dies, Debugger Preset perspective gets displayed
 Switch to perspective of second instance
 Check: Perspective looks ok (docks visible as before)

Task-number: QTCREATORBUG-21083
Task-number: QTCREATORBUG-21669
Task-number: QTCREATORBUG-21668
Task-number: QTCREATORBUG-21813
Task-number: QTCREATORBUG-21851
Task-number: QTCREATORBUG-22110
Task-number: QTCREATORBUG-22169
Task-number: QTCREATORBUG-22189
Change-Id: Ic9eb41ff7699ac0f48a85e68376daa80b2b6847e
Reviewed-by: Robert Loehning <robert.loehning@qt.io>
Reviewed-by: Alessandro Portale <alessandro.portale@qt.io>

src/plugins/debugger/debuggerruncontrol.cpp

@@ -728,8 +728,6 @@ void DebuggerRunTool::stop()
 
 void DebuggerRunTool::handleEngineStarted(DebuggerEngine *engine)
 {
-    EngineManager::activateEngine(engine);
-
     // Correct:
 //    if (--d->engineStartsNeeded == 0) {
 //        EngineManager::activateDebugMode();