Implement built-in classes Vector4, Vector4i and Projection.
* Two versions of Vector4 (float and integer).
* A Projection class, which is a 4x4 matrix specialized in projection types.
These types have been requested for a long time, but given they were very corner case they were not added before.
Because in Godot 4, reimplementing parts of the rendering engine is now possible, access to these types (heavily used by the rendering code) becomes a necessity.
**Q**: Why Projection and not Matrix4?
**A**: Godot does not use Matrix2, Matrix3, Matrix4x3, etc. naming convention because, within the engine, these types always have a *purpose*. As such, Godot names them: Transform2D, Transform3D or Basis. In this case, this 4x4 matrix is _always_ used as a _Projection_, hence the naming.
* Map is unnecessary and inefficient in almost every case.
* Replaced by the new HashMap.
* Renamed Map to RBMap and Set to RBSet for cases that still make sense
(order matters) but use is discouraged.
There were very few cases where replacing by HashMap was undesired because
keeping the key order was intended.
I tried to keep those (as RBMap) as much as possible, but might have missed
some. Review appreciated!
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<>
Improvements:
* Occluder3D is now an abstract type inherited by: ArrayOccluder3D, QuadOccluder3D, BoxOccluder3D, SphereOccluder3D and PolygonOccluder3D. ArrayOccluder3D serves the same purpose as the old Occluder3D (triangle mesh occluder) while the rest are primitives that can be used to manually place simple occluders.
* Occluder baking can now apply simplification. The "bake_simplification_distance" property can be used to set a world-space distance as the desired maximum error, set to 0.1 by default.
* Occluders can now be generated on import. Using the "occ" and "occonly" keywords (similar to "col" and "colonly" for colliders) or by enabling on MeshInstance3Ds in the scene's import window.
Fixes:
* Fixed saving of occluder files after bake.
* Fixed a small error where occluders didn't correctly update in the rendering server.
Bonus content:
* Generalized "CollisionPolygon3DEditor" so it can also be used to edit Resources. Renamed it to "Polygon3DEditor" since it was already being used by other things, not just colliders.
* Fixed a small bug in "EditorPropertyArray" where a call to "remove" was left after the "remove_at" rename.
Fixes some issues found by UBSAN and other misc things:
* Fixed memory leak on exit.
* Properly align ray packet buffer to 64 bytes.
* Added some compiler flags from Embree's build system.
* Fixed ray masks.
Added an occlusion culling system with support for static occluder meshes.
It can be enabled via `Project Settings > Rendering > Occlusion Culling > Use Occlusion Culling`.
Occluders are defined via the new `Occluder3D` resource and instanced using the new
`OccluderInstance3D` node. The occluders can also be automatically baked from a
scene using the built-in editor plugin.
