Entities are being incorrectly added to the index

[ayebear]

When setting components after multi-component indexes have already been created, all the entities with a single component match will be added to each group. This should instead only add entities that contain ALL of the components in the group.

Example of test that should succeed:

let world = new World()
world.entity().set('a').set('b')
assert(world.get('a', 'b').length === 1)
world.get('a', 'b')[0].destroy()
assert(world.get('a', 'b').length === 0)
world.entity().set('a')
assert(world.get('a', 'b').length === 0)
// This throws an assertion error: length is 1, because by creating the entity above, it falsely added it to the index.

// The rest of the test, even though it doesn't even make it here:
world.entity().set('b')
assert(world.get('a', 'b').length === 0)
world.entity().set('b').set('a')
assert(world.get('a', 'b').length === 1)