This removes the bulk of core/editing/*.
The following files remain, because they might be useful yet:
EditingBoundary.h
FindOptions.h
htmlediting.cpp
htmlediting.h
PlainTextRange.cpp
PlainTextRange.h
PositionWithAffinity.cpp
PositionWithAffinity.h
RenderedPosition.cpp
RenderedPosition.h
TextAffinity.h
TextGranularity.h
TextIterator.cpp
TextIterator.h
VisiblePosition.cpp
VisiblePosition.h
VisibleSelection.cpp
VisibleSelection.h
VisibleUnits.cpp
VisibleUnits.h
In addition to remove obviously editing-related stuff like
"ApplyBlockElementCommand.cpp" and "InsertLineBreakCommand.cpp", this
also removes the DOM side of selection, all the caret management and
painting code, composition support (IME) including the relevant
events, spelling checker support, and the undo stack.
Outside the core/editing/* directory, I also deleted the EditorClient,
SpellCheckerClient, and EmptyClients classes. The other changes
outside of editing/ are mostly just about removing mentions of the
selection or carets.
I tried to leave the code for _painting_ selections and composition
runs, though that code is mostly disconnected now.
