Blender Git Loki

First pass at porting mesh_calc_modifiers from DerivedMesh to Mesh

DerivedMesh is almost completely removed from the main loop.

Added `_dep` to dm pointers to make usage of them easy to locate by
searching for `dm_dep`.

Still some work to do. It looks like some of these code paths aren't
entered into, maybe things could be simplified if we can be sure of
whats actually needed.

UI: Fix region_draw_azone_tab_plus missing/broken background.

This was due to the background being drawn by a batch that had its VAO
generated in the windows "UI" context.

Since we use the DRW ogl context to draw the entire area, we have to
regenerate the VAO for thoses UI batches to be drawn correctly.

Port various util functions from DerivedMesh to Mesh

Adds the following functions which are duplicates of
their `DerivedMesh` counterparts:
- `apply_vert_coords`
- `mesh_set_only_copy`
- `create_orco_mesh`
- `add_orco_mesh`
- `calc_weightpaint_vert_array_mesh`
- `mesh_update_weight_mcol`
- `mesh_init_origspace`

Workbench: Show 3D Cursor Overlay

Add modifier_deformVerts_ensure_normals

Same as modwrap_deformVerts but for Mesh

Add BKE_mesh_is_valid

Add modifier_deformVerts_ensure_normals

Same as modwrap_deformVerts but for Mesh

Initialize alpha discard for uiWidgetBaseParameters

No functional change, just playing safe and documenting how to
initialize the parameter in most of the cases.

Workspace: better default for ambient light

Merge branch 'blender2.8' into blender2.8-workbench

Workbench: Shadow groups

- A collection has an override for casting shadows. When not set, the
objects in the collection will not cast any shadows.

Merge branch 'master' into blender2.8

Cleanup: split out extrude spin/screw

Since these will have their own manipulators,
its more convenient to keep them separate.

WM: warn when tool widget not found

This happens when testing adding tools, assert isn't useful.

Cleanup: trailing space

Cleanup: remove axis bounds ifdef

This was added for scale-cage manipulator, but seems generally useful.

Transform: expose 3D center/axis calculation

This is needed for other manipulator placement.

WM: add function to access last_properties

Metaball: pointers used in `DRW_shgroup_call_dynamic_add` don't need to hold the reference.

Armature: Envelope: Small cleanup + don't smooth the distance display.

The actual weighting calculation is not smooth as the bone display.

The bone itself can be smooth for esthetic purpose but the distance display
should match the underlying weighting formula.