Introduce the UndefinedAttribute checker

[karreiro]

Is your feature request related to a problem? Please describe.
When users are type something wrong, like {{ produc }}, Theme Check helps them. However, when users type something like {{ product.availabllle }} nothing happens.

Describe the solution you'd like
Introduce a new UndefinedAttribute checker (similar to the UndefinedObject).

Describe alternatives you've considered
I've considered changing the UndefinedObject checker, but it's actually a different kind of check. Also, it's nice to have this feature in a different checker, then users that don't want this feature can deactivate it.

Additional context
N/A

[charlespwd]

I like this, but I don't know if our type system is rich enough to work in untyped territory. Stuff like metafields rn are all untyped and would show up as UndefinedAttribute. Maybe we have a solution later, but I don't think we have the building blocks for this right now.