Fix T66944: Rigid Body Constraint in duplicated collection is not added to RigidBodyConstraints collection.

We only had a very limited, specific handling of that in collection
duplication code, but this has to be handled at a much more general
level in Object copy code itself, since it makes no sense to duplicate
rigidbody object data without adding new copy to relevant rigidbody
collections...

WARNING: This is a fairly risky rework of rigidbody handling logic
when copying an Object data-block. It is *NOT* considered safe enough
for 2.80 release.

I tried to take into account copy flags to not mess with other IDs
(collections) when we are copying outside of Main, and also not do deg
tags when this is forbidden, but risk of something going wrong here is
too high...

Revert "Fix T64827 (part two): "Batch-Generate Previews" fails with certain files"

This reverts commit 8a5a8282ce48704e60e70cb02d747aede71e70b8.

Fix T64827: "Batch-Generate Previews" crashes.

Second completely unrelated issue reported in same task (tssst...),
caused by missing doversion code of some changes in recent-ish 2.80
development (tsst... again).

Proper fix for the issue (reverted rB8a5a8282ce48 was merely sweeping
the dirt under the carpet...).

Fix T66955: Cannot delete data from file in outliner.

That switch on ID types had not been updated since quiet some time it?d
seem... Using the ID_Type enum type now, so this should not happen again
(compiler will yell at you if you forget to add here any new ID type ;) ).

Also had to change a bit the code layout then, to deal with fake NLA ID
type...

Note that for now, Screen IDs remain excluded from the ID menu usage,
due to T67004.

Merge branch 'master' into asset-engine

Conflicts:
source/blender/editors/space_file/file_ops.c
source/blender/makesrna/intern/rna_space.c
source/blender/windowmanager/WM_api.h

Fix for RC release step to also point at 'current' API doc link.

RC's are supposed to be like "real" releases...

API Doc link: make releases/RC's point to their own version of the doc.

Sounds kind of stupid to have 2.79 pointing to "current" which is now
2.80 API doc... Let's try to avoid that in future.

Fix broken Mesh 'calc_smooth_groups' logic.

We need to check both polygons of a manifold edge to be sure it is
actually smooth...

Reported by Hugo Sales (@someonewithpc) on blender.chat, thanks.

Fix (minor) some typos and other errors in UI messages.

Fix (unreported) UI: useless setting shown for Text data-blocks.

Since we do not have start/end settings for bevel object for Text,
mapping taper to those ends makes no sense here, we can hide that
setting.