Double-clicking an action in Settings > Keymap went straight to the Keyboard Shortcut dialog, where mouse clicks do nothing, so trying to bind Alt+Click there got no reaction. Add Mouse Shortcut was reachable only by right-click.
Double-click and Enter now open the same menu as right-click, at the pointer or the selected row.
Sibling covered: the keyboard dialog no longer inherits mouse recording mode from an earlier Add Mouse Shortcut.
Fixes#2126
