Fix Pose Brush crashing after disabling connected only in FK mode

This function was returning the ik_chain before disabling the
fake_neighbors, so when the brush was used again with fake neighbors
disabled after rebuilding the PBVH and free them, they were still
enabled in the SculptSession, causing a the crash.

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D8195

Sculpt: Mask By Color

This tool generates masks based on the sculpt vertex colors by clicking
on the model, similar to automatic selection tools in image editing
software.

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D8157

Fix T78525: Status bar not reset after Edit Voxel Size

Reviewed By: sergey

Maniphest Tasks: T78525

Differential Revision: https://developer.blender.org/D8181

Fix T77328: Crash on undo Draw Face Sets stroke with dyntopo active

Draw Face Sets does not work in Dyntopo and the sculpt API should be
responsible for that without needing to add checks all over the code,
but it was doing an undo push of type SCULPT_UNDO_FACE_SETS which is not
supported, causing the crash.

Reviewed By: sergey

Maniphest Tasks: T77328

Differential Revision: https://developer.blender.org/D7924

Cleanup: Add functions to check the first brush step and symmetry passes

This adds three functions to check the state of the stroke in the
StrokeCache, removing the references to first_time and
mirror_symmetry_pass from the code. This makes easier to understand what
each code path is doing inside of each tool.

Some tools were using mirror_symmetry_pass incorrectly, so this should
also fix unreported bugs with radial and tiling symmetry related to that.

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D8164

Sculpt: Refactor persistent base to make it usable from other tools

This renames the layer persistent base and adds new API functions to get
the mesh state from the base, so it can be used from other tools and
replaced in the future with a better system.

Reviewed By: sergey

Maniphest Tasks: T77738

Differential Revision: https://developer.blender.org/D8003

Fix T78201: Paint color not matching the UI and color picker

The color picker and brush->rgb values are in srgb, but sculpt vertex
colors works in linear, so they need to be converted.

Reviewed By: sergey

Maniphest Tasks: T78201

Differential Revision: https://developer.blender.org/D8111

Sculpt: Color filter fill mode

This implements a fill mode in the Color Filter tool, which fills the
entire mesh with a specific color.
As this functionality is part of the color filter, this allows to control
the blending of the fill color with the filter strength.

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D8158

Sculpt: Pose Brush option to affect loose parts

This option allows posing meshes with different disconnected elements
using the Pose Brush.

This is achieved by doing the following:
- Creating an ID per vertex that stores the connected component of that vertex.
- By using those IDs, one fake topology connection is created per vertex to the nearest vertex in a different ID. The maximum distance to create that connection is determined by the "Max Element Distance" property. These fake connectivity neighbors are used in the Sculpt API functions iterators, so all the algorithms of the Pose Brush can run without modifications as if everything was part of the same mesh.

In order to make this work, the "Connected only" property of the Pose Brush needs to be disabled. This will add an extra performance cost to the Pose Brush and its preview. To achieve optimal results, max element distance should be as low as possible.

Reviewed By: sergey, campbellbarton

Differential Revision: https://developer.blender.org/D7282

Remove Threaded Sculpt option

Threaded Sculpt is now always enabled by default. If it causes
performance problems compared single threaded sculpt it should be
considered a bug.

Reviewed By: sergey

Maniphest Tasks: T77638

Differential Revision: https://developer.blender.org/D7960