Cleanup: Use MEM_calloc_arrayN in the Cloth Brush

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D8432

Sculpt: Use constraints in cloth deform brushes

Previously, deform brushes were modifying the final positions in the
simulation directly, which was causing all sorts of artifacts in the
deformed area and problems with other features of the solver.
Now these brushes deform a separate array of positions and the solver
adds constraints to them, so the real vertices are moved when solving
the constraints. This prevents those artifacts and gives the brush a
much better behavior.

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D8424

Sculpt: Enable persistent base for the cloth brush

The cloth brush builds the constraints when the stroke starts usign the
current state of the mesh. This means that deformations profuced by the
simulattion will accumulate after multiple strokes as it will always
start from the previous deformed state. While this is useful in many
cases, for other uses it is convenient to always simulate the same
initial shape, but applying different forces to it.

The persistent base options work like the persistent base in the layer
brush and allows the cloth brush to not accumulate deformation after
each stroke. When enabled, constraints are created for the shape stored
in the persistent base instead of from the current state of the mesh.

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D8428

Sculpt: Cloth Brush Soft Body Influence property

This property adds constraints to the simulation using the initial
location of the vertices, making it behave like a soft body. The
strength of these constraints can be modified with the brush parameter.
This makes some deformation modes more subtle and predictable, making it
possible to use the cloth brush to add surface detail in a more
controllable way without loosing completely the original shape of the
mesh.

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D7845

Merge branch 'blender-v2.90-release'

Fix Cloth Brush global Sculpt gravity applied in the wrong falloff

Previously, gravity was only applied in the real brush radius, not in
the whole simulation radius. For most deformation modes, applying
gravity to the entire simulation instead of just to the brush radius and
scaled by the radius (like a regular sculpt brush) makes more sense.
After this fix and with the cloth collisions patch applied, it is possible
to do things like this with the cloth grab brush.

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D8406

Fix T79054: Crash with Cloth Brush and anchored stroke

As the comment says, anchored stroke can't rely on the first stroke
iteration for creating the simulation data. Probably lost in a cleanup.

I also made that anchored stroke doesn't restore the mesh state in the
cloth brush, so it can create the simulation effect.

Reviewed By: sergey

Maniphest Tasks: T79054

Differential Revision: https://developer.blender.org/D8348

Merge branch 'blender-v2.90-release'

Fix Sculpt Relax operation when deforming mesh boundaries

Previously, mesh boundaries were relaxed as any other vertex, which was
causing artifacts and unwanted deformation. In order to prevent this,
the mesh filter was using the automasking system to lock the boundary
vertices, which was hacked into the tool. For the brush, the only
solution was to enable boundary automasking to lock those vertices
in plance.

Now the relax vertex function slides the boundary vertices along the
mesh boundary edges, relaxing all the topology correctly while
preserving the shape of the mesh. The automasking hack in the relax
mesh filter was also removed as now vertices slide correctly along
the boundary.

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D8350

Fix T79074: Mesh Topology info not being updated after changes

All these data arrays are created for a specific topology, so they should be
freed and updated when the PBVH rebuilds. Previously, this was only
happening when freeing the SculptSession, but it also needs to happen in
BKE_sculpt_update_object_before_eval to avoid reusing out of date data.

Reviewed By: sergey

Maniphest Tasks: T79074

Differential Revision: https://developer.blender.org/D8357