Add type hints to sydent/http/servlets

[H-Shay]

This PR request adds type hints to sydent/http/servlets. There were very few docstrings/comments so I did my best to figure out what the types were and add them.

[clokep]

I left one comment which is applicable to the entire PR, besides that I think this seems pretty good though!

[clokep]

I think the main key here is that we should attempt to be a bit more consistent, some of the render_FOO functions return dict, sometimes Dict, sometimes Dict[str, Any] (or even more specific types).

It might help to define a JsonDict = Dict[str, Any] and then import that and return it as we do in Synapse.

[clokep]

Almost there! Just a few minor changes!

[clokep]

Have we been removing the :type: fields in the docstrings as we do this or were we planning to do this afterward?

[H-Shay]

I haven't been removing the :type: fields in the docstrings but I sure can! I'll open another PR to do that though just so I'm not mixing in too many changes in this PR.

[clokep]

I haven't been removing the :type: fields in the docstrings but I sure can! I'll open another PR to do that though just so I'm not mixing in too many changes in this PR.

That sounds like a good plan. (The reasoning to remove them is that there's no reason to encode the same info in two places, especially if one is enforced by a tool -- like mypy -- it tends to get out of date quickly.)