Add env argument to Jinja2Templates, remove **env_options. (ref #2134)

[alex-oleshkevich]

This PR adds env argument to Jinja2Templates class and removes **env_options.

Motivation
See this discussion - #2134

1. arguments of Jinja2Templates configure only this class and nothing else
2. users can configure jinja2.Environment and use it in the app without limits
3. the Environment class may be used by other app components, not just by Starlette

This is a breaking change!

Example

import jinja2
from starlette.templating import Jinja2Templates

env = jinja2.Environment(...)
templates = Jinja2Templates(env=env)

[NickColley]

I like this, it meets the "starlette has a simple opinionated way" need whilst also allowing the user to do something really complicated without the starlette project having to think about a new API at all - since it falls to a shared idea of the Jinja environment which is referenced and used in many different jinja projects.

[Kludex]

Can we deprecate the **env_options first, then remove it on v1?

[Kludex]

Can we overload this?

[alex-oleshkevich]

good idea

[Kludex]

With the overload and the rebase, we are done here 👍

[Kludex]

Suggested change

	self,
	directory: typing.Union[str, PathLike],
	**env_options: typing.Any,
	self, directory: typing.Union[str, PathLike], **env_options: typing.Any

[Kludex]

I've rebased it.

[alex-oleshkevich]

I had to make all other arguments as kw-only to make overloading work.

[Kludex]

Thanks 👍

Let's accept the context_processors being a kw-only as a breaking change.

[Kludex]

I think this doesn't render very well on mkdocs

[alex-oleshkevich]

it looks good

[Kludex]

Ah ok. Great 👍

[Kludex]

Thanks 👍