ComponentDefinition validators are key-specific

[sayhisam1]

Currently, the validators property of ComponentDefinitions is a map from key to function. This means that arbitrary keys cannot be validated.

Proposed changes:

• rename validators -> validator
• validator is now a function that takes in the entire data dict, and returns a bool (similar to t library)

This change also has the neat side-effect of supporting t directly, since users can now pass their t typecheck directly to validator.

I'm not entirely sure what to name the argument - we may want to add support for validating the entity that a component is attached to.