[Notifications] Improve mouse handling

• Make links clickable again
• Don't pass visualParent to context menu as we already give it a position, fixes it being positioned incorrectly
• Open context menu on press already like is done everywhere else
• Give "Copy" the edit-copy icon
• Deselect text after copying again, otherwise it stays selected but the user cannot unselect it.

BUG: 382263
FIXED-IN: 5.10.5

Differential Revision: https://phabricator.kde.org/D7029