Support free text selection and copy/paste by touch events

Qt WebEngineWidgets should allow the selection, copying and pasting of text via touch events. So far only the selection of single words over touch works.

This could be done similar to  

1. First do a long press on a word. The word gets selected.
2. Then allow to fine tune the selection with text sliders
3. Finally, show a context menu containing the "Copy" action

4.Long press in a text input field shows up a context menu containing the "Paste" action.

like  QTBUG-59999 support   Qtwebengine demo  [quicknanobrowser ], test ok.

     Support free text selection and copy/paste by touch events, url below

  https://github.com/qt/qtwebengine/tree/dev/examples/webengine/quicknanobrowser

but we want to support webenginewidgets , like simplebrowser alse be supportted , url below

https://github.com/qt/qtwebengine/tree/dev/examples/webenginewidgets/simplebrowser