Some actions, such as select trivial connection, don't need the
user to choose which trace at a corner to start from -- either
one will do. Same for moving a simple trace corner.
Likewise, Edit in Footprint Editor shouldn't ask if you mean the
footprint or the pad. Obviously it's the footprint.
This change adds a CLIENT_SELECTION_FILTER which allows clients
to do tool- or action-specific filtering of the selection before
the disambiguation menu is run.
It also removes some tool- and action-specific code which was
in the selection_tool and shouldn't have been.
Fixes: lp:1708869
* https://bugs.launchpad.net/kicad/+bug/1708869