Adds a new, cleaned up, HashMap implementation.
* Uses Robin Hood Hashing (https://en.wikipedia.org/wiki/Hash_table#Robin_Hood_hashing).
* Keeps elements in a double linked list for simpler, ordered, iteration.
* Allows keeping iterators for later use in removal (Unlike Map<>, it does not do much
for performance vs keeping the key, but helps replace old code).
* Uses a more modern C++ iterator API, deprecates the old one.
* Supports custom allocator (in case there is a wish to use a paged one).
This class aims to unify all the associative template usage and replace it by this one:
* Map<> (whereas key order does not matter, which is 99% of cases)
* HashMap<>
* OrderedHashMap<>
* OAHashMap<>
* Very old macros from the time Godot was created.
* Limited arguments to 5 (then later changed to 8) in many places.
* They were replaced by C++11 Variadic Templates.
* Renamed methods that take argument pointers to have a "p" suffix. This was used in some places and not in others, so made it standard.
* Also added a dereference check for Variant*. Helped catch a couple of bugs.
It used to always cycle all the peers when checking which one needed to
be notified, now it only does that when the target is multiple (i.e.
broadcast or exclusion).
It used to check if a net_id was ever assigned to that node to detect
when to send the path confirm to the remote peer.
This is wrong, because the same net_id is shared for all the remote
peers, but sent one by one.
Instead we now check if it's either not assigned or if the assigned
net_id is a cache ID, and in that case ensure that the remote peer has
been notified.
This can be further improved by unifying the cache interface, but for
now it's a fast fix to get path-only sync to work.
Now uses two interfaces so it can be overridden in the future, and
core no longer depends on Node.
The interfaces are implements in scene/multiplayer.
Replaces root_node with root_path.
Remove all Node references from MultiplayerAPI.
Initial implementation of the MultiplayerReplicationInterface and its
default implementation (SceneReplicationInterface).
New MultiplayerSpawner node helps dealing with instantiation of scenes
on remote peers (e.g. clients).
It supports both custom spawns via a `_spawn_custom` virtual function,
and optional auto-spawn of known scenes via a TypedArray<PackedScenes>
property.
New MultiplayerSynchornizer helps synchronizing states between the local
and remote peers, supports both sync and spawn properties and is
configured via a `SceneReplicationConfig` resource.
It can also sync via path (i.e. without being spawned by a
MultiplayerSpawner if both peers has it in tree, but will not send the
spawn state in that case, only the sync one.
