Take the X position of the lines into account when navigating up and
down by lines, so we end up at the right x-pos also for centered and
right-aligned lines.
- hide the generated "empty" menu item in the IM submenu
- pause/resume the text tool around all selection/cursor/buffer changes
(fixes most drawing artifacts)
This has several advantages:
- it's always readable, no matter how sick font/colors are.
- it does not mess up the buffer, which is a model that should not
contain temporary edit states.
- preediting does not clutter undo.
- it fixes the remaining bugs in the old preediting code because that
code is completely gone now.
- Reset the IM context in much more situations, like on button_press
and when the text editor is initialized and halted (pretty much what
GtkTextView does).
- As a consequence, halt the rectangle text tool after the text tool
in control() because cancelling the IM preedit might cause a
re-framing of the layer because it resized.
- pause()/resume() the draw tool around gimp_text_tool_halt() so we
definitely avoid drawing atrifacts when the text tool is shut down
in the middle of an IM preedit. That pause/resume pair should have
been there from the beginning actually.
- most importantly, when the text changes and we set the buffer (as
happens when undoing), block the "changed" signal on the *buffer*
and not on the proxy (which doesn't even have a "changed"
signal). This was apparently something that happened during the
on-canvas editor merging.
- don't update the proxy when the layout changes, that's the wrong way
around. Instead, update the layout whenever the proxy changes,
remove lots of calls to update_layout() from the text editor and let
the "changed" callback on the buffer do its job of updating
everything.
Feed them into the text editor's IM context and into the proxy text
view's key bindings. Fixes input methods (e.g. entering of unicode
sequences seems to work flawlessly now).
