Implement RFE 6147: move infantry loading to interface and allow cargo bays

[Sleet01]

1. Moves some data from InfantryBay.java into InfantryTransporter.java, a new Interface that should provide the minimum functionality for an Infantry-loading bay.
2. Implement missing Infantry drop prerequisites to align with TW and SO rules.
3. Remove restriction on number of infantry units dropped per turn, per SO rules.
4. Add the ability to load Infantry units (but currently no others) to CargoBay.java
5. Return ability to use Cargo Container bays to Fighter units (this had worked but was broken by the Mounted changes)
6. Removed unused entity builders from AreaEffectHelperTest.java while adding them for CargoBayTest.java.

See https://discord.com/channels/458705327911731231/1344135419180351560 for rationale for some design decisions taken here.

Testing:

• Many manual drops to confirm UI, space usage, and unit compatilibity.
• Added unit tests for CargoBay class.
• Ran all three projects' unit tests.

Merging this should unblock MegaMek/mekhq#5929

Close #6147

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 29.16%. Comparing base (b03a2d9) to head (0833748).
Report is 43 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##             master    #6627    +/-   ##
==========================================
  Coverage     29.15%   29.16%            
- Complexity    15415    15444    +29     
==========================================
  Files          2865     2871     +6     
  Lines        280027   280232   +205     
  Branches      49307    49335    +28     
==========================================
+ Hits          81655    81717    +62     
- Misses       192890   193030   +140     
- Partials       5482     5485     +3     

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[psikomonkie]

Nice! I'm really excited for this. Code-wise everything looks great. Missing license file on CargoBayTest.java will need added, and I think the javadoc for InfantryTransporter.java was copied from Transporter.java - I was confused by it for a moment while reviewing, so maybe that should be looked at.

Thanks!

[psikomonkie]

Should this be updated? I think even including a reference to Transporter (@see Transporter) would help someone unfamiliar with MM's transport system.

[psikomonkie]

License?

[psikomonkie]

There are a few more Transporters that are for transporting infantry, and I think the changes to MovementDisplay.java would prevent units from dropping out of these Transporters:

• InfantryCompartment.java
• BattleArmorBay.java

I don't think this should be implemented for the BA Handles even though those are for Transporting infantry, since this is specifically for infantry that are using their weight for loading.