Every call to g_type_create_instance() currently will incur a RWLock at
least once, but usually twice to test for both G_TYPE_FLAG_ABSTRACT and
G_TYPE_FLAG_DEPRECATED.
Additionally, each call to g_type_instance_free() also checks for these.
That results in a synchronization of GTypeInstance creation across all
threads as well as being a huge amount of overhead when creating instances
like GskRenderNode.
With this patch in place, the next two biggest issues are
g_type_class_ref() and g_type_test_flags() not getting inlined within
gtype.c in release builds. We can address that separately though.
Sysprof shows that the RWLock, with this patch in place, falls off the
profiles.
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