Missing high-level event handling for text editing and navigation events

Many text-editing operations can be performed in multiple ways, for instance selecting text (both keyboard and mouse events trigger this).

However, there is no virtual interface at all to handle all these user interactions, no matter where they come from (i.e. reimplementing key-event handling is not sufficient in the example above), which makes it very errorprone and difficult to do (one practically has to read qtextedit.cpp to see what is done when).

A high-level, text editing-specific QEvent type would solve this problem. This could also be done for QLineEdit.