Implement an Sample-Distribution Shadow Mapping filter

[ScottPeterJohnson]

Sample-Distribution Shadow Mapping (SDSM) is a technique for dynamically fitting the shadow maps of a shadow filter to the depth samples that will be needed, resulting in improved shadow quality.

This commit adds the option to use a SdsmDirectionalLightShadowFilter in place of a regular DirectionalLightShadowFilter. Usage requires GL 4.3+ support.

I don't think this is 100% ready for merging immediately, but it does work. I've been told there might be code for compute shaders coming, in which case this can be adapted to use that instead of somewhat kludgily inventing its own wheel. There's a lot around handling specific GL 4.3+ APIs (for example this needs compute shaders) that I'm not sure engine wants to do it.

Mentioned on the forums here:
https://hub.jmonkeyengine.org/t/reducing-shadow-motion-issues/49289/3

Included is a TestSdsmDirectionalLightShadow sample app. I was using a stripped down version of the Sponza model to test lighting, but it's still pretty big and it didn't seem like large test data gets included in PRs. It's available here, and goes in the jme3-examples directory alongside "town.zip": https://drive.google.com/file/d/18mmwRPe--gskuWjfBfv9nB-dCSzfa1eB/view?usp=sharing

Example with SDSM:

Example without SDSM:

(Note that some parts of the translation from Kotlin to Java I delegated to Claude Code, so if there are still some uselessly verbose parts I didn't catch those can be fixed.)