maya: Allow more than three eggObjectTypes in a Maya model

[darktohka]

Issue description

As of right now, a Maya group node can contain three egg object types: eggObjectTypes1, eggObjectTypes2 and eggObjectTypes3. Some nodes may have more than three object types set. These are lost during the maya2egg conversion process.

Solution description

Instead of checking eggObjectTypes1, eggObjectTypes2 and eggObjectTypes3 for object type information, we will now check all attributes matching eggObjectTypes[1...inf]. As soon as we find an egg object type that is not set in this fashion, we will stop looking for object types to add to the group. This approach is backwards compatible.

The eggObjectFlags.mel Maya script has also been changed to allow more than 3 object types to be added. eggObjectFlags.mel is responsible for adding one egg object type to a group node. Before this commit, it would print a warning if more than 3 object types are present, but now, it will find the first empty object type slot to insert an object type into, removing this 3 object type limitation.

Checklist

I have done my best to ensure that…

• …I have familiarized myself with the CONTRIBUTING.md file
• …this change follows the coding style and design patterns of the codebase
• …I own the intellectual property rights to this code
• …the intent of this change is clearly explained
• …existing uses of the Panda3D API are not broken
• …the changed code is adequately covered by the test suite, where possible.

[rdb]

Thanks, looks good.

[codecov]

Codecov Report

Merging #1134 (4cacaf3) into master (51b6a90) will increase coverage by 0.00%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #1134   +/-   ##
=======================================
  Coverage   16.08%   16.08%           
=======================================
  Files        3728     3728           
  Lines      360298   360298           
=======================================
+ Hits        57965    57967    +2     
+ Misses     302333   302331    -2     

Impacted Files	Coverage Δ
panda/src/pgraph/lightAttrib.cxx	31.92% <0.00%> (+0.32%)	⬆️

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