Expose `_RequestOptions` as a public member

### Is your feature request related to a problem?

I'd like to add type annotations for functions that accept keyword arguments that are passed to the `ClientSession.request` method. aiohttp has a TypedDict for this already, `_Requestoptions` but it's a protected member of the aiohttp.client module (has a leading underscore and is not declared in `__all__`).

### Describe the solution you'd like

Remove the underscore for `_RequestOptions` and add it to the `__all__` list, or create a version of the typed dict that includes the kwargs that are part of the documented API.

### Describe alternatives you've considered

There's probably a good reason why it's private, but I didn't see a GitHub issue that addressed that question. If There's a good reason, document the answer here.

### Related component

Client

### Additional context

_No response_

### Code of Conduct

- [x] I agree to follow the aio-libs Code of Conduct