Since the introduction of multi-select, we have had both `on_selection`
and `on_selection_change`, the latter of which was only invoked when a
change in selection came in through the model.
This removes `AbstractView::on_selection` and replaces it usage with
the more explicit `on_selection_change` everywhere.
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
Modifying the selection while holding the shift button and selecting
with the mouse or the arrow keys no longer results in broken selections.
Fixes#6279.
Rather than invalidating the entire window, which is very expensive on
the transparent desktop widget, just invalidate the areas that actually
need updating.
