Moved to a system using variadic templates, shared with CallableBind.
New code is cleaner, faster and allows for much better optimization of core
type functions from GDScript and GDNative.
Added Variant::InternalMethod function for direct call access.
Remove _sort_children from script bindings:
_sort_children is an internal method which shouldn't be exposed to scripts.
Added support for non-bound methods in MessageQueue:
So we can use deferred calls without exposing internal methods to scripts.
Added debug checks in CallableCustomMethodPointer:
Adding method pointer callables to the message queue was causing crashes
in case an object was destroyed and the same memory was allocated for
another one. The new object had a valid object id but the call was erroneous.
Release will be fixed later, along with Variant which has the same problem and
is also fixed for debug only.
Which means that reduz' beloved style which we all became used to
will now be changed automatically to remove the first empty line.
This makes us lean closer to 1TBS (the one true brace style) instead
of hybridating it with some Allman-inspired spacing.
There's still the case of braces around single-statement blocks that
needs to be addressed (but clang-format can't help with that, but
clang-tidy may if we agree about it).
Part of #33027.
Also implemented decal atlas, so projectors and other stuff can be added.
Sidenote: Had to make RID hashable, so some unrelated includes changed
in order to include it in hashfuncs.h
Was missed in #36393 because no `callable_mp()` calls were actually
compiled with `tools=no` in that PR.
Also work around GCC warning that also affects the
`call_with_variant_args_ret_helper` variant.
