Unify syntax with Smithy metadata

[kubukoz]

Smithy has a concept of metadata, and it uses pretty similar syntax to what I've chosen for SmithyQL. While SmithyQL is its own language and has other concepts, it'd be nice if metadata/query inputs used the same syntax for most things.

There's one major difference that I know of without deeply investigating: SmithyQL uses = for key-value pairs, whereas Smithy metadata uses :. SmithyQL should start supporting either (with = being a deprecation, automatically rewritten on formatting).