Cycles Denoising: Get rid of halos around bright edges

Previously, bright edges (e.g. caused by rim lighting) would sometimes get
halos around them after denoising.

This change introduces a log(1+x) highlight compression step that is performed
before denoising and reversed afterwards. That way, the denoising algorithm
itself operates in the compressed space and therefore bright edges cause less
numerical issues.

Render: Use GHash for storing render parts

Previously, render parts were stored in a linked list and every tile update
searched the entire list for the correct part. As a result, the overhead
of searching tiles increased quadratically w.r.t. the number of tiles.

By hashing the parts based on their location, this operation is much faster,
significantly reducing the tile update overhead for small tiles and/or large
renders.

For example, rendering an empty scene in 1080p at 1spp and 8x8 tiles goes
down from 9.22sec to 1.45sec on my laptop.

Reviewers: brecht, sergey

Differential Revision: https://developer.blender.org/D4896

Cycles: add colorspace manager class and utilities based on OpenColorIO

This is the groundwork for supporting loading image textures with arbitrary
color spaces through OpenColorIO.

Initial patch by Lukas, completed by Brecht.

Differential Revision: https://developer.blender.org/D3491

Cycles: support loading images from arbitrary OpenColorIO color space

These are the internal changes to Cycles, for Blender integration there are no
functional changes in this commit.

Images are converted to scene linear color space on file load, and on reading
from the OpenImageIO texture cache. 8-bit images are compressed with the sRGB
transfer function to avoid precision loss while keeping memory usages low. This
also means that for common cases of 8-bit sRGB images no conversion happens at
all on image loading.

Initial patch by Lukas, completed by Brecht.

Differential Revision: https://developer.blender.org/D3491

Revert "Squashed D3203: Baking system overhaul: Move baking settings from render settings into BakePasses"

This reverts commit d04aa1fd44db55422d84bc23f54cc4753ec2b06b.

Squashed D3203: Baking system overhaul: Move baking settings from render settings into BakePasses

Merge remote-tracking branch 'origin/master' into experimental-build

Cycles: add animation denoising Python operator.

This adds a cycles.denoise_animation operator, which denoises an animation
sequence or individual file. Renders must be saved as multilayer EXR files
with denoising data passes.

By default file path and frame range come from the current scene, and EXR
files are denoised in-place. Alternatively, a different input and/or output
file path can be provided.

Denoising settings come from the current view layer. Renders can be denoised
again with different settings, as the original noisy image is preserved along
with other passes and metadata.

There is no user interface yet for this feature, that comes later.

Code by Lukas with modifications by Brecht. This feature was originally
developed for Tangent Animation, thanks for the support!

Differential Revision: https://developer.blender.org/D3889

Cycles: add animation denoising Python operator.

This adds a cycles.denoise_animation operator, which denoises an animation
sequence or individual file. Renders must be saved as multilayer EXR files
with denoising data passes.

By default file path and frame range come from the current scene, and EXR
files are denoised in-place. Alternatively, a different input and/or output
file path can be provided.

Denoising settings come from the current view layer. Renders can be denoised
again with different settings, as the original noisy image is preserved along
with other passes and metadata.

There is no user interface yet for this feature, that comes later.

Code by Lukas with modifications by Brecht. This feature was originally
developed for Tangent Animation, thanks for the support!

Cycles: animation denoising support in the kernel.

This is the internal implementation, not available from the API or
interface yet. The algorithm takes into account past and future frames,
both to get more coherent animation and reduce noise.

Ref D3889.