Supporting spawning Prototype Variants

[jkeon]

For a given Definition, there may be multiple Prototypes that fit that definition as "Variants".

They are not structurally different (same components etc) but their values differ such that general configuration is not sufficient and it's better to duplicate an existing prototype instead.

Ex. RenderMeshes which have a bunch of SharedComponents to point to the right Mesh/Material combo.

What is the current behaviour?

• There is no support for allowing a Variant to be chosen for a given definition.
• You'd have to make more specific definitions which doesn't scale.

What is the new behaviour?

• You can optionally choose to register a Prototype with a Variant key.
• The Variant keys are PrototypeVariant structs (which are just wrapped ints) to allow for Burst to work without polymorphism.

What issues does this resolve?

• None

What PRs does this depend on?

• None

Does this introduce a breaking change?

• [ ] Yes
• [x] No

[jkeon]

Most changes made, some conversations still to be had.

[mbaker3]

Responded/resolved

[jkeon]

@mbaker3 Ready for last review