install_deps: Update llvm to 12.0 (with minimal now being 11.0).

Ref T88438.

install_deps: Update OIIO to 1.1.15.1.

Ref. T88438.

Cleanup: OSL buildlib patch: Remove `.rej` part.

This patch contained changes for an `.rej` rejection file generated by
failed patch apply... Definitly nothing to do here.

install_deps: Update OSL to 1.11.14.1.

This has been a huge pain to get working, for several reasons (new flags
needed, patching is now mandatory, etc.).

Further more, discovered that debian OIIO package is now silently
relying on OpenCV, without even proper handling of this dependency (at
least in the `-dev` package), so had to revert to force-build own OIIO
again on that distro for the time being.

Ref. T88438.

install_deps: update OIDN to 1.4.1, and ISPC to 1.16.0.

Ref. T88438.

BlenRead: Add GHash-based search for already read linked IDs.

Ths commit adds a new `IDNameLibMap` to `Main`, used during file reading
to quickly find already read linked IDs.

Without that, search would use string-based search over list of linked
data, which becomes extremely slow and inneficient in cases where a lot
of IDs are linked from a same library. See also {T89194}.

Extrem-usecase reported in T89194 is now about 4 times faster in linked
data reading (about 2 times faster for the whole .blend file loading).

More normal cases (like Sprites studio production files) have barely
measurable speed improvements, a few percents at best.

NOTE: `main_idmap` API was extended to support insertion and removal of
IDs from the mapping, avoids having to re-create the whole thing several
time during libraries expansion in readcode.

Differential Revision: https://developer.blender.org/D11757

Fix LibOverride crashing in some cases where reference linked data gets MIA.

When the root of an override hierarchy disapears, there is no way to do
a proper resync, just abort.

Reported by studio, thx.

Fix (studio-reported) liboverride resync crash after recent changes.

Recent own rBabf3ce811f6e prevented any LayerCollection update during
the whole liboverride resync process, for both performances and feature
reasons.

However that means that the various runtime caches like the Base GHash
are not cleared anymore during ID remapping process, so we need to call
`BKE_main_collection_sync_remap` instead of `BKE_main_collection_sync`
when we finally are ready for this update.

Reported by @eyecandy (Andy Goralczyk) from Blender studio, thanks!

LayerCollection: Refactor of resync-with-Collection-hierarchy process.

The goal of this refactor is to improve resync of LayerCollections
hierarchy to match again Collection one.

Current code would destroy and re-create valid layers whenever a parent
collection would be removed, which leads to losing way too often
layer-related settings when editing collection hierarchies.

While this could be partially addressed from operators side, there was
no way to fix those issues from lower level, more generic ID management
code like ID remapping or library override resync processes.

The new code builds a shallow wrapper around existing (aka old) layers
hierarchy, does a set of checks to define the status of all existing
layers, and try to find the closest matching unused layer in cases where
layers and collections hierarchies do not match anymore.

The intent is to both re-use as much as possible existing layers, and
to pick the 'best' possible layer to re-use, following those heuristics:
* Prefer layers children of current one first (in old hierarchy), and only
use those from other higher-level hierarchies if no (grand-)child is found.
* Prefer to use closest layers available in the old hierarchy.

NOTE: The new code is about 12%-15% slower than the previous one, which is
expected given the increased complexity. Note that this would not be an
issue in practice if this code was not called way too often (needs to
be converted to lazy update instead, which is a long known TODO).

NOTE: The LayerCollectionResync code uses its own built-in version of
FIFO queue, as performances in this code is currently a critical point
(it can get called tens of thousands of times during a single (heavy)
ID management operation currently, in a production file e.g.).

Differential Revision: https://developer.blender.org/D12016

Remove the code in `BKE_collection_move` to preserve LayerCollection flags.

This code was actually buggy (forcefully re-enabling excluded layers in some
cases).

Further more, it should not be needed now that layerCollection resync code
reuses as much as possible existing layers instead of deleting and
re-creating them all the time.

Differential Revision: https://developer.blender.org/D12016