LibOverride: Fix resync bug on recursive overrides.

Linked override were not properly ignored in some part of the code,
leading to invalid resync results in some cases with recursive overrides
(i.e. overrides of overrides).

Reported by Andy @eyecandy from the studio.

LibOverride: Fix (unreported) assert when creating overrides of linked overrides.

We do not want to copy exiting overrides data from linked ID when
creating its local override (be it either a template, or because linked
ID is itself an override of another lib data).

Note that this was not a very serious issue, would just cause some memory
leak since override data is re-created on newly copied local data
anyway.

These use cases have been very little tested so far, but both complex
production pipeline and future restrictive workflow will make them fairly
common...

LibOverride: Add own flag to copy or not overrides to ID copy code.

Relying on only no-main for that was weak, and inn the end it turns out
we sometimes also need to ifnore override data during copy of Main
data-blocks.

NOTE: The new `LIB_ID_COPY_NO_LIB_OVERRIDE` is also added to the
`LIB_ID_COPY_LOCALIZE` set of flags.

NOTE: The fact that we may now copy liboverrides in some non-main cases
may cause issues in some cases, pretty impossible to track all possible
ones from reading the code... Would not expect too many problem though,
usages of `LIB_ID_CREATE_NO_MAIN` by itself are not so common.

LibOverride: Fix several issues with resync code.

This commit essentially touches to post-processing of collections and
objects after resync itself has been done, to ensure their proper
instantiation in the scene:

- Remove a lot of the process in resync case (resynced data are assumed
to be already instantiated in the scene, unlike override creation
case).

- For auto-resync, only do post-processing once after all overrides
have been resynced (doing it after each individual resynced was
causing a lot of instantiation glitches, with a lot of unwanted
extra objects and collections being added to the master collection).

It also deals in a much more reliable way with detection of objects
missing from the scene, by using the new `BKE_scene_objects_as_gset`
utils.

As a bonus this makes auto-resync process slightly faster (only by a few
percents, but that's always good to get).

Outliner Override: Tweak to order of error messages.

Cleanup: Typos in comments.

BKE_collection: Add a util returning a gset with all objects in given scene's collections.

This is internaly using the code of `BKE_scene_objects_iterator` and
steals its gset. More efficient than using that iterator directly to
rebuild another GSet...

Minor cleanup to `scene_collection_array`.

Use array allocation, and remove useless check.

Outliner: regroup more type of entries under a single icon.

In folded view, some type of data are listed as one icon per item,
others are 'compacted' as a single icon with a counter.

This commit adds bones (edit, normal and pose ones), pose groups and
vertex groups as 'compacted' ones in folded view.

Part of D10855.

LibOverride: Add a dedicated view in the Outliner.

This is a minimal, information-only view currently, listing by default
all the override data-blocks, with their user-edited override
properties.

System-generated overrides (like the overrides of pointers to other
override data-blocks) can be shown through a filter option.

Finally, potential info or warning messages from (auto-)resync propcess
are also shown, as an icon + tooltip next to the affected items.

Part of D10855.