Merge branch 'blender-v2.82-release'

Partial Fix T73043: Denoising Albedo not working well for Sheen

Similar to the Microfacet Closures, the Principled BSDF Sheen closure is
added at a high weight but typically results in fairly low values.
Therefore, the default weight is a bad indicator of importance.

The fix here is the same as it was back then for Microfacets:
Compute an average weight using the normal as the half-vector
and use it to scale down the sample weight and the albedo channel.

In addition to drastically improving denoising of materials with
sheen when using the new Denoising node, this also can reduce noise
on such materials considerably.

Merge branch 'blender-v2.82-release'

Fix T73133: UDIM texture count in Eevee is limited by OpenGL

Based on @fclem's suggestion in D6421, this commit implements support for
storing all tiles of a UDIM texture in a single 2D array texture on the GPU.

Previously, Eevee was binding one OpenGL texture per tile, quickly running
into hardware limits with nontrivial UDIM texture sets.
Workbench meanwhile had no UDIM support at all, as reusing the per-tile
approach would require splitting the mesh by tile as well as texture.

With this commit, both Workbench as well as Eevee now support huge numbers
of tiles, with the eventual limits being GPU memory and ultimately
GL_MAX_ARRAY_TEXTURE_LAYERS, which tends to be in the 1000s on modern GPUs.

Initially my plan was to have one array texture per unique size, but managing
the different textures and keeping everything consistent ended up being way
too complex.

Therefore, we now use a simpler version that allocates a texture that
is large enough to fit the largest tile and then packs all tiles into as many
layers as necessary.

As a result, each UDIM texture only binds two textures (one for the actual
images, one for metadata) regardless of how many tiles are used.

Note that this rolls back per-tile GPUTextures, meaning that we again have
per-Image GPUTextures like we did before the original UDIM commit,
but now with four instead of two types.

Reviewed By: fclem

Differential Revision: https://developer.blender.org/D6456

Cleanup: clang-format

Image Editor: Initialize Add Tile options from current tile

Previously, non-default alpha or float settings had be set manually.

With this change, the Add Tile and Fill Tile operators initialize
width, height, alpha and float from the currently selected tile
if it has a vaild ImBuf, otherwise from the first tile.

Cleanup: clang-format

Cycles: Use OIIO UDIM tag instead of %04d

Cycles: Support UDIMs with OSL shading

Cleanup: Remove BLI_stringenc_path