Debugger: Infrastructure for reworked native mixed debugging

- Remove old experimental native mixed approach.
- Move some common stack parsing to Stackhandler.
- Mark gdbbridge.py debug output explicitly to remove it
  from actual reponse handling

New native mixed needs QtDeclarative changes and
QTC_DEBUGGER_NATIVE_MIXED=1 for now.

Change-Id: I09eed1da51cea878636d36756015b7bfaed34203
Reviewed-by: Christian Stenger <christian.stenger@theqtcompany.com>

src/plugins/debugger/debuggerengine.h

@@ -117,6 +117,8 @@ public:
     // Used by AttachCrashedExternal.
     QString crashParameter;
 
+    bool nativeMixedEnabled = false;
+
     // For Debugger testing.
     int testCase = 0;
 };
@@ -443,6 +445,9 @@ protected:
 
     void updateLocalsView(const GdbMi &all);
     void checkState(DebuggerState state, const char *file, int line);
+    bool isNativeMixedEnabled() const;
+    bool isNativeMixedActive() const;
+    bool isNativeMixedActiveFrame() const;
 
 private:
     // Wrapper engine needs access to state of its subengines.