Fix T83275: Crash with scene statics and empty scene

ob can be NULL, so it needs to be checked before accessing ob->mode

Differential Revision: https://developer.blender.org/D9680

Fix sculpt transform incorrently flipping displacement in Y and Z axis

These functions were only checking the X axis for flipping the
displacement for a symmetry area depending on the initial position of
the pivot.
This affects transform and any other tools that transform vertices and
applies symmetry based on areas (the pose brush, for example).

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D9654

UI: Add Sculpt Session info to stats

This adds the vertex and face count info to the scene stats in sculpt
mode. These stats count the active vertices and faces in the
sculptsession for the active object. This has the following advantages:
- It is possible to know how many vertices the sculptsession has active
comparted to the vertex count of the entire scene from sculpt mode
- When sculpting with constructive modifiers, these stats will report the
number of vertices that you can actually sculpt with, instead of the
vertex count of the modified mesh and the entire scene.

Reviewed By: sergey, dbystedt

Differential Revision: https://developer.blender.org/D9623

Sculpt: Refactor transform code to allow incremental updates

This adds support for incremental updates in the sculpt transform
code. Now tools can define if they need the displacement applied
for the original coordinates or incrementally.

This is needed for features like elastic transform or cloth deformation
target in the transform tool.

No functional changes.

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D9547

Fix Edit Face Set operator not being cancelled when the cursor is not over the mesh

If the cursor is not over the mesh, the operator was still using the
last Face Set ID updated by the drawing cursor code when the cursor was
over the mesh.

This now cancels the operator instead of modifying a Face Set that will
look random to the user.

Reviewed By: sergey

Differential Revision: https://developer.blender.org/D9545

Rename use paint symmetry to use mesh symmetry in quadriflow

The original name was chosen because symmetry was a property of
the Paint struct. Now symmetry is a property of meshes, which
also makes the name of the property easier to understand.

Reviewed By: sergey, dbystedt

Differential Revision: https://developer.blender.org/D9618

Fix wireframe opacity creating artifacts on sculpt overlay edges

When lowering the wireframe opacity with sculpt overlays enabled, the
wireframe overlay was creating white artifacts along the edges.

Reviewed By: fclem

Differential Revision: https://developer.blender.org/D9607

Fix T82586: Sculpt normals not updating with EEVEE enabled

The root cause of this bug is that the function that updates the PBVH
normals is drw_sculpt_generate_calls. As now both the overlays and
mesh can be drawn without using pbvh drawing, the normals were not
updating. This patch forces a normals updates also in the no PBVH
drawing code path of the overlays. This was affecting both shading and
sculpt surface sampling in both flat and smooth shading modes.

Having the sculpt normals being updated by the drawing code is a wrong
design which also causes other issues like:

Brushes that sample the surface and do multiple stroke steps between

redraws will sample invalid normals, creating artifacts during the
stroke clearly visible in some brushes.

Brushes that do not need to sample the surface update the normals on

each redraw. This affects performance a lot as in some cases, updating the
normals takes more time than doing the brush deformation. If flat shading
is being used, this is only necessary to do once after the stroke ends.

Reviewed By: fclem
Differential Revision: https://developer.blender.org/D9535

Merge branch 'blender-v2.91-release'

Fix T82542: Boundary brush crash with dyntopo

This brush needs to be disabled for dyntopo as it stores its custom data
and deforms from original coordiantes.

Reviewed By: sergey

Maniphest Tasks: T82542

Differential Revision: https://developer.blender.org/D9516