Fix T79929: crashes with Cycles denoising on older Macs

This was a bug in OpenImageDenoise, upgrade to latest 1.2.3 which has the fix.
This in turn required a newer ispc version.

Differential Revision: https://developer.blender.org/D8892

Fix T78793, T79707: Cycles crash on macOS with older CPUs

Embree static libraries need additional linking flags to avoid SSE and
AVX symbols getting mixed up.

Fix OpenCL render error in large scenes

In scenes such as Cosmos Laundromat, there were memory allocations bigger than
2GB which would overflow.

Problem and solution found by AMD, thanks!

CMake: clean up setting of platform specific linker flags

Set flags directly on the target, and use common function for all cases.
This refactoring helps with the next commit for test executables.

Ref D8714

Tests: bundle tests for some modules in their own executables

The ffmpeg, guardedalloc and blenlib are quite isolated and putting them in
their own executable separate from blender_test is faster for development than
linking the entire blender_tests executable.

For Cycles, this also bundles all the unit tests into one executable.

Ref T79958

Differential Revision: https://developer.blender.org/D8714

CMake: clean up setting of platform specific linker flags

Set flags directly on the target, and use common function for all cases.

Tests: bundle tests for some modules in their own executables

The ffmpeg, guardedalloc and blenlib are quite isolated and putting them in
their own executable separate from blender_test is faster for development than
linking the entire blender_tests executable.

For Cycles, this also bundles all the unit tests into one executable.

I also considered going back to having every test file in its own executable,
but the size of these executables does add up quickly, and linking and running
all blenlib tests is still < 1s here.

Ref T79958

Reviewed By: LazyDodo

Maniphest Tasks: T79958

Differential Revision: https://developer.blender.org/D8714

Fix T80630: potential crash in volume grids in Eevee shaders

Found by address sanitizer.

Fix build error after clog color printing changes

Geometry: add .attributes in the Python API for Mesh, Hair and Point Cloud

This puts all generic float/int/vector/color/string geometry attributes in a new
.attributes property. For meshes it provides a more general API for existing
attributes, for point clouds attributes will be used as an essential part of
particle nodes.

This patch was implemented by @lichtwerk, with further changes by me. It's
still a work in progress, but posting here to show what is going on and for
early feedback.

Ref T76659

Differential Revision: https://developer.blender.org/D8200