Panda3d-simplepbr

Fix running on Python 3.9

* BREAKING: Change exposure setting to match Panda3D value/usage
* shader: Fix shadow artifact when a light has a zero spotCosCutoff (e.g., point lights)
* shader: Fix `tonemap.frag` ignoring alpha value
* ibl_funcs_cpu: Reduce how often solid angle is calculated when getting SH coefficients
* ibl_funcs: Switch from functools.lru_cache to functools.cache
* utils: Switch from a cube to a full-screen quad for make_skybox()

* Use a constant shadow bias and switch shadows to using front faces
* Add support for calculating the blue/Z channel of a normal map in the shader
* Fix IBL reflection vector (was using view-space vector instead of world-space)
* Fix 330 shaders being used when not requested
* Some fixes for WebGL (GLSL ES)
* Fix duplicate definition in `tonemap.frag` that could cause compile errors
* Fix potential compile issue with non-330 shaders when calculating shadow contributions
* Explicitly disable sRGB for HDR framebuffer
* Fix IBL lagging behind by a frame

* Fix `use_330` defaulting to `True` instead of `None`

* Add support for post-tonemap, SDR, color LUT transform
* Add support for using HDR cubemaps for IBL diffuse and specular
* Add `simplepbr` `DirectNotify` category to provide better control over logging
* Add type annotations and mark package as being typed
* Add `simplepbr.utils.make_sky_box()` to create a skybox `NodePath` from a cubemap texture
* Add support for setting initial Pipeline parameters from PRC config variables
* Default `enable_shadows` to True
* Fix using `texture2D/3D()` instead of `texture()` when using GLSL 330 shaders
* Fix error when a `DisplayRegion` is missing a camera
* Fix shadows being delayed by a frame
* Fix `TextNode.set_text_color()` not working
* Fix possible divide-by-zero in Smith GGX visibility function (fixes some visual artifacts)
* Fix metallics not responding to ambient lighting
* Fix possible shader compile error for duplicate defines
* Fix objects rendering black if they do not have a material (there is now a default material)
* Fix `ShowBase.set_background_color()` not working after `simplepbr.init()`

* Fix normals when using hardware skinning
* Fix hardware skinning when using GLSL 120 shaders
* Stop enabling the auto shader on TextNodes
* Improve performance of get_all_casters()
* Fix gl_FragColor warnings for shadow and tonemap shaders
* Bundle shaders into a shader.py module when building wheels