Insidious waypoint command change in Plan view

#### Issue details
In Plan view, if a waypoint has focus in the table, an accidental arrow down key press or mouse wheel down action will change the dropdown selection from WAYPOINT to RTL, which could have severe consequences if uncaught by the user (actually happened on a Rover, and a user's mower went on a mildly destructive path until he caught it and emergency stopped).

Steps to reproduce:
Create a mission of any number of waypoints.
Mouse click on a waypoint in the table (or tab to focus on the command dropdown).
Arrow key or mouse wheel down changes the dropdown selection (could be very insidious).

Not sure if there's a way to "prevent default" or similar, as with web apps, but that would be the ideal solution - force an actual dropdown list selection vice "hotkey" selection.

Relevant Discord discussion:
https://discord.com/channels/674039678562861068/797946854792757259/1245948112510517248

#### Version
1.3.81, build 1.3.8914.1508 (though likely has existed for years)

#### Platform
[ ] All
[ ] AntennaTracker
[x ] Copter
[ x] Plane
[ x] Rover
[ x] Sub

#### Airframe type
All

#### Hardware type
All

#### Logs
N/A

Start by reproducing the issue in Mission Planner's Plan view using a mission with waypoints, focusing the waypoint command dropdown before pressing Arrow Down or scrolling. Trace the Plan view control that handles the focused dropdown; done means accidental keyboard or mouse-wheel input no longer changes WAYPOINT to RTL, while deliberate dropdown selection still works.

Written by the indexing model from the issue text.