Fix 5204: Fighter Squadron weapon crits and group damage application

[Sleet01]

This fixes the NPE caused when Capital Fighters take weapon crits; it also:

• completes the missing squadron addition functionality (required to properly get the FighterSquadron back from a single Capital Fighter in the squadron);
• implements part of the currently-broken Squadron-wide damage application (used for tracking damage for MekHQ purposes, reportedly).

The other problem from that issue, Warships unable to engage at Medium or greater range, could not be reproduced and was likely fixed in a previous PR.

TODO: There is still a lot of work to do on Capital Fighters:

1. Weapon crits may or may not actually halve the damage for wings after a Weapon Critical is applied.
2. I have no idea how to split units off from a Squadron other than letting them die.
3. It looks like arbitrary squadron sizes are allowed, but I have not confirmed this yet.
4. Unknown how well single-fighter Capital Fighters will actually operate.

Testing:

• Ran all 3 projects' unit tests
• Loaded the failing save in 0.49.18, exported the units as MULs, loaded into 0.49.19 with and without fixes for comparison

Close #5204

[BLR-IIC]

The other problem from that issue, Warships unable to engage at Medium or greater range, could not be reproduced and was likely fixed in a previous PR.

This was apparently fixed in #5195 . Nice job here!