Problem:
Since right-click can now show a popup menu, we can provide messaging to
guide users who expect 'mouse' to be disabled by default. So 'mouse' can
now be enabled by default.
Solution:
Do it.
Closes#15521
Problem:
1. Right-click does not work in statusline unless you left-click first (to focus
the statusline).
2. Modifier (e.g. shift+rightclick) does not work in statusline.
Solution:
Make clickable statusline sections receive right-clicks regardless of whether
the statusline is focused.
Closes#18994
