Fix i18n utils_cli mistake.

Reported by James Monthea (@jmonteath), thanks.

Fix broken 'undocumented' case in registration of Macro opertators.

Code dealing with macro operators missing description field was slightly
different than the one from Operator registration.

This lead to invalid memory accesses in some python introspection cases
like the i18n messages extraction code in `bl_i18n_utils` module.

Fix some mesh edition macro operators incorrectly setting an empty description string.

No operator or macro should be missing description. But if they do, then
they should use NULL pointer, and not an empty string.

This behavior was already enforced (through an assert) for operators,
previous commit made it the same for macros.

Cleanup: LayerCollection resync: Proper `r_` prefix for return function parameter.

Cleanup: LayerCollection resync code.

Mainly naming (also droping the `layer_collection` in favor of just
`layer` for internal code, this is clear enough and much shorter). Add
proper parent/child identifiers, `r_` prefix for parameters also used as
return values, etc.

Also made some parameters const.

Cleanup: Layer resync: Split object/base resync part in own function.

No behavioral change expected here.

Cleanup: Turn PointCache flags defines into an anonymous enum.

Fix T89771: Cloth disk cache is not read on library overrides in some cases.

Issue would happen when the original, linked data already had 'Disk Cache'
setting enabled. Override would then see no difference with linked data,
and not create any rule for it (as expected).

Root of the issue was that in Cloth modifier copy code, those disk cache
settings were not copied at all, so every time local overrides were
re-generated by copying linked data, those flags would be reset to their
default values.

NOTE: this might exist in other PointCache usages as well, but this code is
in such a bad state that I'd rather do minimal strictly needed changes
there, on a case-by-case basis. Proper recode of that whole system is
wayyyyy out of scope here.

Fix (unreported) LibOverride diffing generating operations for non-editable properties.

Non-pointer-like properties that are not editable should never generate
override operations.

While harmless (those would never be applied back anyway), better not
clutter override operations list, and also enjoy the symbolic
performances improvement here.

NOTE: Pointer-like properties (pointers and collections) remain
processed as usual here since they usually imply recursivity. We could
make an exception to the exception for ID pointers, but for now I don't
think this is worth it.

Rename Scene's embeded collections from "Master Collection" to "Scene Collection"

Note that this name is essentially never used anywhere, besides as 'information'
mostly accessible from python console. Those embedded IDs are not in Main, so they
are not accessible by name ever, and mostly unusable from animation perspective
(either drivers or fcurves).

Therefore, no breakage is expected in user scripts or addons, nor when
loading in older versions of Blender.

Reviewed By: dfelinto, brecht

Differential Revision: https://developer.blender.org/D11812