Extracted from 14281

Extracted from 14281

* frontends/WorkArea:
  - processKeySym(): new method that should be used by all frontends
    instead of buffer_view_->workAreaKeyPress().
* frontends/qt4/GuiWorkArea:
  - keyPressEvent(): call WorkArea::processKeySym() instead of
    buffer_view_->workAreaKeyPress().
* frontends/gtk/GWorkArea.C:
* frontends/qt3/QContentPane.C:
  - call WorkArea::processKeySym() instead of
    buffer_view_->workAreaKeyPress()

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@14383 a592a061-630c-0410-9148-cb99ea01b6c8