There were two ways of specifing selected text for a highlight depending
on whether it was a "single word" or text selected using hold-and-pan.
In addition to being a bit more complicated than is necessary, with the
addition of the language support plugin system (where the "single word"
selected might be expanded), it makes more sense to simply use the same
logic and table structure for both cases.
The dictionary lookup special case (hold-without-pan triggering a
dictionary lookup by default) still works as before.
In addition, this patch fixes a minor inefficiency during dictionary
quick lookup -- before this patch, the highlight would be re-selected
because the quick lookup window is run concurrently and tries to fetch
ReaderHighlight.selected_text but this is set to nil immediately after
triggering the lookup. This is unnecessary because :clear() will be
called anyway when the quick pop-up closes, and so clearing this can be
left until then.
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>