Refactor ideas

[kristiker]

• IKeyValueCollection ContainsKey(k) && GetProperty(k) -> GetValueOrDefault(k) like in ParticleDefinitionParser
• LoadFile(file+ "_c") -> LoadFileCompiled(file)

[xPaw]

Renderer: try to run update of both normal and skybox scenes before renderer, then try to also do all morph rendering before main rendering.

[xPaw]

Replace rawVertices float array and EnsureSpaceForVertices in particle renderer with ArrayPool.Shared.

EDIT: done

[xPaw]

Refactor particles trails/sprites to have more in common, then merge the separate shaders into one spritecard shader.