Cleanup Compositor AA: remove redundant initialization

Cleanup: use one class for edge detection in Anti-Aliasing node

Merge remote-tracking branch 'origin' into compositor-anti-aliasing

Merge remote-tracking branch 'origin' into compositor-anti-aliasing

Conflicts:
source/blender/blenlib/intern/math_base_inline.c

Cleanup: replace NULL with nullptr - use brackets around if

Merge remote-tracking branch 'origin' into compositor-anti-aliasing

Compositor Anti-Aliasing: addressed comments from code review

- Made node slightly larger to make text fit
- Renamed "Local Contrast Adaptation Factor" to "Contrast Limit"
- Removed unused enum
- Style: added brackets around if
- Style: Ran make format (excluded changes from unrelated files)

Merge remote-tracking branch 'origin' into compositor-anti-aliasing

Cleanup: Compositor anti-aliasing: rename and delete unused variables

Compositor anti-aliasing: map values between 0 and 1

expose values in ranges between 0 and 1 to user

Compositor: Add Anti-Aliasing node

This is an implementation of Enhanced Subpixel Morphological Antialiasing (SMAA)

The algorithm was proposed by:

Jorge Jimenez, Jose I. Echevarria, Tiago Sousa, Diego Gutierrez
Homepage URL:

http://www.iryoku.com/smaa/
This node provides only SMAA 1x mode, so the operation will be done with no spatial multisampling nor temporal supersampling.

Here is a comparison between existing antialiasing (Scale3x, imported from GIMP) and the Anti-Aliasing Node (SMAA 1x):

SMAA 1x produces much higher quality results than Scale3x.
The existing AA operation seems to be used only for binary images by some other nodes. Using SMAA for binary images needs no important parameter such as "threshold", so we perhaps can switch the operation to SMAA, though that changes existing behavior.

Currently, the node has 3 options:

threshold
local contrast adaptation factor
corner rounding
Please refer to devtalk thread for discussion about interface: https://devtalk.blender.org/t/compositor-anti-aliasing-node-d2411/17570

Example: Using Anti-Aliasing Node as an alternative of OLM smoother that is widely used in Japanese animation studios:

Notes:

The program code assumes the screen coordinates are DirectX style that the vertical direction is upside-down, so "top" and "bottom" actually represent bottom and top, respectively
smaa_areatex.cpp is a stand-alone software I [Shinsuke Irie] wrote for another project, so its copyright is still owned by me and under MIT-style license, see https://github.com/iRi-E/smaa-cpp
Unfortunately, this patch doesn't include OpenCL support (I'm not familiar with it...), though SMAA is not so slow
Tested on macOS 11.2.1