It should help with scrolling the dockable to make the widget visible,
as I don't see a generic and simple scrolling API for GTK scrollable
containers.
In my own testing, it did work if the dockable was already opened. But
if it was just created by the blink API, then giving focus immediately
doesn't properly scroll. I am not really going to investigate now, but
this should be fixed eventually.
This function will help us raise attention to various widgets in
dockables by blinking them similarly to how we blink locks or visibility
icons.
I associate this with the fact that property widgets identifier will be
the property name, so we get identifiers for free when creating widgets
through the propwidgets API.
Use this for the alpha lock brought by GimpLayerTreeView.
Also use the new gimp_widget_blink_rect() to only blink the appropriate
cell when a lock is preventing you from doing something.
Add gimp_tools_blink_lock_box() utility function, in a new
gimptools-utils.c file, which takes a GimpItem, and blinks the
GimpItemTreeView lock-box of the corresponding dockable. This can
be used to hint that the item's lock toggles are preventing it from
being edited.
