Add :recursive selector function

[mtdowling]

Closes #2228

Background

• Adds a recursive selector function to do things like check if a shape has a specific mixin or if a shape is in the hierarchy of a resource.

Testing

• Added selector tests, and manually tested

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The following example finds all shapes that have a specific mixin:

:test(:recursive(-[mixin]->) [id=smithy.example#Foo])

The following selector finds shapes that are contained within the resource hierarchy of a specific resource.

resource :test(:recursive(<-[resource]-) [id=smithy.example#Baz])

The following selector finds all shapes that directly or transitively target a specific shape, essentially the inverse of ~>.

[id=smithy.example#MyShape] :recursive(<)

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