Validate in split_entity_id

[balloob]

Breaking change

Custom component authors: split_entity_id will now raise a ValueError if the passed value does not follow the basic entity ID format (<domain>.<object id>). Previously it could return a list with a single item.

Proposed change

Validate it's a valid entity ID and not return data that violates the type signature.

I noticed that our validator would crash if the entity ID was invalid when I stumbled upon this commit: zachowj/node-red-contrib-home-assistant-websocket@d085ef4#diff-ada8264180728098ca920091eca5641fd9a97221543fa087a9cec21b488c3de3R258-R267

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[balloob]

@bdraco I think you added validating domains like this. Is this ok to change so split_entity_id doesn't raise?

[bdraco]

That should be fine. All it cares about is that is the left side.