Fix up and re-enable UAV support for major attacks and HQ attacks

[jaj22]

What type of PR is this.

1. Bug
2. Change
3. Enhancement

What have you changed and why?

The UAV support that reveals targets for major attacks and HQ attacks was accidentally disabled at some point in the 3.0+ process. I have simplified, optimized and re-tested it.

The principle was that attacks often stall or take an excessive time because they can't see enemies in buildings. The UAV-reveal gives them an assist, which should give them half a chance of dealing with hidden units.

Please specify which Issue this PR Resolves.

closes #3466

Please verify the following and ensure all checks are completed.

1. Have you loaded the mission in LAN host?
2. Have you loaded the mission on a dedicated server?

Is further testing or are further changes required?

1. No
2. Yes (Please provide further detail below.)

[Tiny-DM]

Still looking into #3249 which should include a split for attack and support UAVs. This should be fine to do first though.