Show tooltips when hovering over links in mouse selection modes as well.

Previously, these tooltips were only shown in "Browse mode".
This patch adds them for "Selection", "Text selection", and
"Trim selection" as well.  These are the modes where the cursor
changes to a hand when hovering over a link.

BUG: 397783

Differential Revision: https://phabricator.kde.org/D15123