RFC: Tags as first-class citizens

[hmans]

Summary:

So far we've been modeling tags as normal components that always have a value of true, with miniplex providing both a Tag type and constant, both equal to true. But what if we made tags first-class citizens of the library?

• Would make the API around tags clearer
• and also a bit more flexible, since tags don't need to exist as components in the Entity type

Checklist:

• [ ] Provide addTag and removeTag functions
• [ ] Keep a list of the entity's tags in the __miniplex component
• [ ] Index tagged entities (can we reuse Archetype here?)
• [ ] Remove Tag constant and type