Debugger: Rework step{In,Out,Over} handling

Main menu action pass operation to current engine, everything else
is handled there.

Combine execute{Step,Next} and execute{Step,Next}I functions.
Implementation were mostly similar, in some cases unneeded
(the instruction-wise version e.g. for Python)

Drop GDB-isms 'step', 'next' in favor of 'step in' and 'step over'.

Change-Id: I232232bc7a67d9d297a74f1c81dc43be96787d34
Reviewed-by: David Schulz <david.schulz@qt.io>
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

src/plugins/debugger/qml/qmlengine.h

@@ -72,11 +72,9 @@ private:
 
     void resetLocation() override;
 
-    void executeStep() override;
+    void executeStepOver(bool) override;
+    void executeStepIn(bool) override;
     void executeStepOut() override;
-    void executeNext() override;
-    void executeStepI() override;
-    void executeNextI() override;
 
     void setupEngine() override;
     void runEngine() override;