feat: BillboardControl optimization + javadoc + reduce object allocations

[capdevon]

This PR introduces significant performance optimizations, a new constructor for easier initialization, and comprehensive documentation for the BillboardControl class.

Key Changes & Improvements:

• New Constructor:
  • Added a constructor BillboardControl(Alignment alignment) that allows specifying the initial billboard alignment directly upon instantiation. This simplifies common usage patterns.
• Performance Optimization:
  • Replaced new Quaternion() with a reusable tempQuat instance in rotateScreenAligned() to reduce per-frame object allocations, thereby minimizing garbage collection pauses and improving overall frame rate stability.
• Code Quality & Maintainability:
  • Added comprehensive Javadoc comments to the class, its methods, and member variables. This improves code readability, makes the control easier to understand, and facilitates future maintenance and development.
• Demo:
  • Updated the TestBillboard class to demonstrate the functionality of the optimized BillboardControl and its various alignment options at runtime.

These changes ensure the BillboardControl remains functionally identical while significantly improving its runtime efficiency and developer experience.

[richardTingle]

In the example, how is the yellow quad supposed to behave. Even in JME today it behaves weirdly (so not your change) but I want to understand what it is supposed to do (it doesn't seem to billboard, just flip between two different orientations)

[capdevon]

In the example, how is the yellow quad supposed to behave. Even in JME today it behaves weirdly (so not your change) but I want to understand what it is supposed to do (it doesn't seem to billboard, just flip between two different orientations)

That's a good question about the yellow quad's intended behavior. Honestly, I'm not entirely sure what its original purpose was or how it's supposed to behave. I've encountered a fair amount of code in the jME core module that seems redundant, incomplete, or a bit strange, and this might be another instance of that.

From my perspective, the most useful and commonly utilized behaviors are Alignment.Screen (for true billboarding) and Alignment.AxialY (for rotation around the Y-axis).