Add a proper scope type for `"inside"`

[pokey]

It will be a cascading scope type (#1045) combining the following:

One of the constituent scope types will be just be surrounding pair, but where we ask pair for inside before returning it in getTarget(); domain is just the surrounding pair

The other constituent scope type is a tree-sitter syntactic scope handler with a tree-sitter pattern that languages can define however they want. For example, Python would define it to be body

Note that the "inside" modifier won't just be simply containing instance of this new scope. It will first take its input target and see if it has an interior attribute. If so, it will use it, if not it will be containing instance of this scope