Merge branch 'master' into temp-ghash-experiments

Note that 'store hash' feature was removed for now - to complex to maintain (conflicts)
and relatively easy to re-add if we ever really want this one day.

Conflicts:
source/blender/blenlib/BLI_ghash.h
source/blender/blenlib/intern/BLI_ghash.c
source/blender/blenlib/intern/hash_mm2a.c
source/blender/bmesh/tools/bmesh_region_match.c
tests/gtests/blenlib/BLI_ghash_performance_test.cc
tests/gtests/blenlib/BLI_ghash_test.cc
tests/gtests/blenlib/CMakeLists.txt

Merge branch 'master' into temp-ghash-experiments

Merge branch 'master' into temp-ghash-experiments

Merge branch 'master' into temp-ghash-experiments

Merge branch 'master' into temp-ghash-experiments

Merge branch 'master' into temp-ghash-experiments

Making hash storage optional.

This required quite a bit of work, but storing hashes for 'simple' very quick
hashing/comparison functions is stupid (loss of space, and even introduces a
very small slow down), while with e.g. strings (which comparison and hasing
is quite expansive), it gives huge speedup (twice quicker insertion, about
33% quicker on lookup).

This makes lower-level code a bit less clear, since we add one 'child type' of Entry
for each case (GHash/GSet, and storing hash or not), but this also has the benefit
of being stricter when accessing entries' members...

Cleanup (reduce a bit passing size of entries around by storing it in ghash itself).

GTests GHash performance cleanup (strictly one test per GTest).

Factorize gset/ghash add/reinsert functions.

Merge branch 'master' into temp-ghash-experiments

Merge branch 'master' into temp-ghash-experiments

Merge branch 'master' into temp-ghash-experiments

Grrr, thought I had added that file already!

GHash: Add difference and symmetric_difference (with tests).

Also fix some issues in previous commits.

Notes about our 'symmetric_difference':
* name is taken from py, but our function takes multiple arguments,
and returns keys which are present in one and only one given ghash.
So we may want a better name for that
(real symmetric difference only accepts/works with two args)!
* Its code is a bit more complex than the others, think it's worth it though,
XOR is a really useful operation imho.

GHash: add intersection (with tests).

GHash: add Union operations (with tests).

Minor optimization to strcmp hash helper - if both pointers are the same, then strings are the same...

GHash: add copy/isdisjoint/isequal/issubset/issuperset, with gtests.

We still need union/intersection/difference/symetric_difference...

Fix crashing GHashIterators.

Inlined accessors are using a another struct than Entry itself,
those two must match perfectly!

Also fix a few other minor typo/mistakes, and come back to modulo
bucket-hashing for now.