Add a decorator that will parse request arguments from the view function's type annotations.

I've built a working proof of concept of this idea in webargs-starlette.

@app.route("/")
@use_annotations(locations=("query",))
async def index(request, name: str = "World"):
 return JSONResponse({"Hello": name})

A marshmallow Schema is generated from the annotations using Schema.TYPE_MAPPING to construct fields.

The code for use_annotations mostly isn't tied to Starlette and could be adapted for AsyncParser (and core.Parser when we drop Python 2 support).