Fix T51057 Modifiers lose bevel weight and crease

This is for 2.80 (though bug I mistakenly merged into was for 2.78.
Duplicate bugs T58127, T58411, T58440, and T58789 all fixed.
Bevel weights and crease are not real Mesh layers so get lost
on coversion of mesh to bmesh unelss the mesh's cd_flag member
tells the converter to create layers for them.
Most code the copies or partially copies meshes uses
mesh_new_nomain_from_template_ex, so copied the flag there.

Partial fix for T58113 bevel harden normals bug.

This fixes the problem where not all faces got hardened properly
when using a hardening mode in the bevel modifier.

Partial fix for T57868, crash when using bevel from Python.

These changes are necessary. Need to mark vertices of edges passed
in geom; also the normals.out slot has a custom element type, not
ELEM, so need to prevent attempt by python code to convert it to
an elem. But this leaves a memory leak. I will rework code to not
use normals.out slot at all, but that's a bigger fix.

Now there is a crash in a different place (GPU code). Think that if
using Op on its own (instead of from edbm_bevel_calc, there needs to
be a dependency graph update and maybe more?

Fix T57850, bevel modifier crash with vertex groups and face area mode.

Used wrong Loop variable in this case.

Fix 'Set and Use 3D Cursor' normal editing command.

Was missing a return of OPERATOR_RUNNING_MODAL for that subcommand.

Fix bevel crash T56287, when face strength goes to 1.

Fix bevel problem for vertex-only cube corners.

Was introduced by code from gsoc branch that does better job
on cube corners, but shouldn't have applied to vertex-only case.

Quiet warnings in bmesh_bevel.c.

Fix T55490, intersect two triangles fails.

Need to use the 'use_partial_connect' option in island connect,
so changed signatures of various functions to pass that into and
then down from BM_mesh_intersect (making true for intersect, false
for boolean).
Then fix bm_face_split_edgenet_partial_connect to work when
input edges are not necessarily wire, but at least not in the
face they are being connected in. That caused generalization
of core BM_vert_separate_hflag_wire (which is only used in
this one place in all Blender).

For 2.8, bring back debug mode indices display.