RFC: Use annotations for parsing arguments

Nobody has claimed this yet.

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](https://github.com/sloria/webargs-starlette).

```python
@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).

Start by reviewing the proof of concept in webargs-starlette, then inspect AsyncParser and core.Parser and how marshmallow Schema.TYPE_MAPPING constructs fields. Done means adapting the annotation-based use_annotations approach for the relevant parsers so request arguments are parsed from view-function annotations.

Written by the indexing model from the issue text.