Instead of updating all viewports, then blitting all viewports
to the backbuffer, then swapping all buffers, we run through
all viewports and render, blit, and swap backbuffer before
going to the next viewport.
Fixes include using proper depth buffer format in 3D (this had previously been fixed already but the changes were lost in a rebase), Remove unused lighting and shadowing code in 2D, and update 2D UBOs using glBufferSubData so that they remain the appropriate size.
Using this command:
```
find -name "thirdparty" -prune -o -name "*.h" -exec sed -i {} -e '/return /! s/\t\([A-Za-z0-9_]* \*[A-Za-z0-9_]*\)\;/\t\1 = nullptr;/g' \;
```
And then reviewing the changes manually to discard the ones that don't
seem correct/safe/good (notably changes to `core` unions).
This allows light sources to be specified in physical light units in addition to the regular energy multiplier. In order to avoid loss of precision at high values, brightness values are premultiplied by an exposure normalization value.
In support of Physical Light Units this PR also renames CameraEffects to CameraAttributes.
Per-light energy gives more control to the user on the final result of
volumetric fog. Specific lights can be fully excluded from volumetric fog
by setting their volumetric fog energy to 0, which improves performance
slightly. This can also be used to prevent short-lived dynamic effects
from poorly interacting with volumetric fog, as it's updated over several
frames by default unless temporal reprojection is disabled.
Volumetric fog shadows now obey Light3D's Shadow Opacity property as well.
The shadow fog fade property was removed as it had little visible impact
on the final scene's rendering.
At this time, it works best in the Vulkan Renderers as they support using multiple samplers with the same texture.
In GLES3 this feature really only allows you to use the screen texture without mipmaps if you want to save the cost of generating them.
This can be used to make shadows translucent for a specific light.
The light distance fade system also uses this to smoothly fade the shadow
when the light fade transition distance is greater than 0.
`shader_uniform` is now consistenly used across both per-shader
and per-instance shader uniform methods. This makes methods easier
to find in the class reference when looking for them.
