QmlDebugger: user input on watches

src/plugins/debugger/debuggerengine.cpp

src/plugins/debugger/debuggerengine.h

src/plugins/debugger/debuggerplugin.cpp

src/plugins/debugger/gdb/gdbengine.cpp

src/plugins/debugger/gdb/gdbengine.h

src/plugins/debugger/qml/qmlcppengine.cpp

src/plugins/debugger/qml/qmlcppengine.h

src/plugins/debugger/qml/qmlengine.cpp

src/plugins/debugger/qml/qmlengine.h

src/plugins/debugger/watchhandler.cpp

src/plugins/debugger/watchwindow.cpp