Consider adding an extra with just httpx

[jonathanberthias]

Hello,

As a user of Starlette, I have had to add httpx to my (test) requirements to be able to run tests with the TestClient, despite never directly importing anything from httpx.

There is already an extra called full which would install httpx, but that would also install itsdangerous, jinja2, python-multipart and pyyaml, none of which I need.

Would you consider adding another extra that would provide only httpx with the correct bounds? Perhaps it could be called testclient or simply httpx.

Thanks!

[Kludex]

I don't think it's necessary. Maybe someone created a PR with it in the past, may be worth checking what was the decision back then.