Modified polygon management to make it more compatible with MoltenVK

Added support for Sprite, AnimatedSprite and Polygon2D (should add for tileset eventually).

They should now allocate memory in blocks and reuse the same
memory every time the item is cleared and redrawn.

This should improve performance considerably.

Removes antialiased flag for draw_* methods.

Still a lot to do

This should make it easier to obtain the data directly from an Image

-Texture renamed to Texture2D
-TextureLayered as base now inherits 2Darray, cubemap and cubemap array
-Removed all references to flags in textures (they will go in the shader)
-Texture3D gone for now (will come back later done properly)
-Create base rasterizer for RenderDevice, RasterizerRD

* Implements a growing chunked allocator
* Removed redudant methods get and getptr, only getornull is supported now.

-Added VulkanContext
-Added an X11 implementation
-Added a rendering device abstraction
-added a Vulkan rendering device abstraction
-Engine does not work, only shows Godot logo (run it from bin/)

Prevent Visual Studio compiler throwing C4715: not all control paths return a value.

Prevents GCC compiler throwing: control reaches end of non-void function.
Prevents Visual Studio throwing C4715: not all control paths return a value.

Prevents GCC compiler throwing: control reaches end of non-void function.
Prevents Visual Studio throwing C4715: not all control paths return a value.

Fix Visual Studio throwing C4996 warning in ustring.cpp.

Add ConfigFile::parse()

Allow to use arrow keys with TOOL_MOVE

[Mono] Basis/Transforms array operator comments and improvements

Fix selectable locked items

Remove AnimationTreePlayer node

Fixes a crash in the 2D editor

The behavior for Basis and Transform2D is unchanged, and Transform gets new behavior. All of the behavior is identical to GDScript's behavior. 

Integrated the new `NavigationServer` and `NavigationServer2D`

Allow per pixel transparency in javascript platform

- Added Navigation Agents and Obstacles.
- Integrated Collision Avoidance.

This work has been kindly sponsored by IMVU.