Disable gravity in Draw Face Sets brush

Applying gravity to this brush does not make much sense and undo/redo
won't work correctly as it uses a different undo type.

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D7925

Fix Sharpen mesh filter in Multires

Instead of accumulating displacement for each vertex into the neighbors, accumulate the opposite displacement from each neighbor into the vertex. I think this is the same and it does not produce artifacts in Multires.

Reviewed By: sergey, brecht

Differential Revision: https://developer.blender.org/D7508

Fix T76776: Implement vertex_visibility_get for PBVH_GRIDS

This was missing from when Face Sets were enabled in Multires, so it was
always considering that all vertices in the grids are visible. This
should also fix other unreported bugs.

Reviewed By: sergey

Maniphest Tasks: T76776

Differential Revision: https://developer.blender.org/D7809

Cleanup: Always use pbvh in PBVH BKE files

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D7889

Sculpt: Improve twist axis in Pose FK mode

Previously, the twist rotation was aligned using the stroke location.
This was causing unexpected results when rotating some Face Sets rigs.
Now the intersection with the first Face Set in the flood fill is used,
which produces much better results.

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D7900

Cleanup: Remove unused grab delta in Pose Brush

The grab delta is not used in do_pose_brush_task_cb_ex, so there is no
reason to add it to SculptThreadedTaskData

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D7901

Sculpt: Cloth Filter

This tool is similar to the cloth brush, but it applies the cloth
simulation deformation to the whole mesh in an uniform way. The
simulation can be controlled using the mask to pin vertices and the face
sets to define force action areas.

It uses the same solver as the cloth brush which now no longer depends
on StrokeCache.

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D7857

Sculpt: Pose Brush Face Sets FK mode

This Pose Brush origin mode simulates an FK deformation in the entire
model when clicking on the face sets, as they were controls of a fully
rigged character. Combined with the previous Face Sets modes that allow
creating IK chains, the pose brush should now be able to simulate most
of the common rigs deformations.

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D7839

Fix mesh filter using the wrong face set as active

This was returning the wrong face set in cases where the active vertex
has more than one available face set.

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D7858

CD_PROP_COL datalayer

This implements a generic color datalayer and its functions. Based on
D5975.

Reviewed By: brecht

Differential Revision: https://developer.blender.org/D7838