* Replace license text in headers with SPDX identifiers.
* Remove specific license info from outdated readme.txt, instead leave details
to the source files.
* Add list of SPDX license identifiers used, and corresponding license texts.
* Update copyright dates while we're at it.
Ref D14069, T95597
* Spot lights are now handled as disks aligned with the direction of the
spotlight instead of view aligned disks.
* Point light is now handled separately from the spot light, to fix a case
where multiple lights are intersected in a row. Before the origin of the
ray was the previously intersected light and not the origin of the initial
ray traced from the last surface/volume interaction.
This makes both strategies in multiple importance sampling converge to the same
result. It changes the render results in some scenes, for example the junkshop
scene where there are large point lights overlapping scene geometry and each
other.
Differential Revision: https://developer.blender.org/D13233
BVH2 triangle intersection was broken on the GPU since packed floats can't
be loaded directly into SSE. The better long term solution for performance
would be to build a BVH2 for GPU and Embree for CPU, similar to what we do
for OptiX.
Remove prefix of filenames that is the same as the folder name. This used
to help when #includes were using individual files, but now they are always
relative to the cycles root directory and so the prefixes are redundant.
For patches and branches, git merge and rebase should be able to detect the
renames and move over code to the right file.
