Restore overlay depth drawing which was removed in [0].
For viewport navigation this is useful. Disable overlays
for other operations such as painting & object placement.
Also disable color drawing in the overlay_next engine drawing
when drawing depth, since it caused the viewport to show a
checkered backdrop.
Details:
A boolean argument has been added to ED_view3d_depth_override instead
of new enums in eV3DDepthOverrideMode since mixing object-filtering
and draw-type in the one enum gets verbose & awkward, where most
existing enums would have needed to include NO_OVERLAY in their name.
V3D_DEPTH_NO_OVERLAYS has been renamed to V3D_DEPTH_ALL,
the caller must pass in use_overlay as false.
[0]: 5fea1eda36
ababc2e01b