Add asynchronous views.

[Mariusz Felisiak]

Add asynchronous views in Django (see ​details).

Accepted based on ​DEP 0009: Async-capable Django.

​PR

[Mariusz Felisiak <felisiak.mariusz@…>]

In 1e858adf:

Refs #31224 -- Added BaseHandler.check_response().

[Mariusz Felisiak <felisiak.mariusz@…>]

In 17009e9:

Refs #31224 -- Added autoconversion of test async methods.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 40a64dd1:

Refs #31224 -- Doc'd async adapter functions.

[Mariusz Felisiak <felisiak.mariusz@…>]

In 8d4638db:

[3.0.x] Refs #31224 -- Doc'd async adapter functions.

Backport of 40a64dd1e24d45f8e00a55b22a5174b8f1359b5c from master

[Mariusz Felisiak <felisiak.mariusz@…>]

In fc0fa72f:

Fixed #31224 -- Added support for asynchronous views and middleware.

This implements support for asynchronous views, asynchronous tests,
asynchronous middleware, and an asynchronous test client.

[GitHub <noreply@…>]

In b5ad450f:

Refs #31224 -- Removed incorrect @sync_to_async(thread_sensitive=True) example.

It does not support thread_sensitive when used as a decorator, yet.

[Mariusz Felisiak <felisiak.mariusz@…>]

In d292d11:

[3.0.x] Refs #31224 -- Removed incorrect @sync_to_async(thread_sensitive=True) example.

It does not support thread_sensitive when used as a decorator, yet.
Backport of b5ad450fa6d53186b68f89a4507fdbabc8900f74 from master

[GitHub <noreply@…>]

In d94a9aa:

Refs #31040, Refs #31224 -- Prevented cycles in exceptions chain.

Async exception handling was raising an exception that was creating a
cycle in the exception chain (by re-raising an exception in
sync_to_async that was already being handled).

Thanks Chris Jerdonek for detailed analysis.

[Mariusz Felisiak <felisiak.mariusz@…>]

In bd389a8:

[3.1.x] Refs #31040, Refs #31224 -- Prevented cycles in exceptions chain.

Async exception handling was raising an exception that was creating a
cycle in the exception chain (by re-raising an exception in
sync_to_async that was already being handled).

Thanks Chris Jerdonek for detailed analysis.
Backport of d94a9aa0557a459a5b9b7b82a8c043de14f8b1a0 from master

[Carlton Gibson <carlton@…>]

In 8d59075:

Refs #31224 -- Made sync_to_async() examples use thread sensitive with ORM calls.

[Carlton Gibson <carlton.gibson@…>]

In f36c441f:

[3.1.x] Refs #31224 -- Made sync_to_async() examples use thread sensitive with ORM calls.

Backport of 8d59075184f4cd2852b374359850ff7aeb412ec1 from master

[nessita <124304+nessita@…>]

In 3614ce2:

Refs #31224 -- Fixed typo in django/test/client.py.