Old browser versions that do not support websockets have long since
faded from use.

This is the public interface, but when the resolver argument was added
it was only added to the supporting WebSocketClientConnection class.

docs: Add release notes for 6.3

Use SPDX license identifier

Use SPDX license identifier: Apache-2.0
This will help tools to produce valid SPDX.
Signed-off-by: NMarc-Etienne Vargenau <marc-etienne.vargenau@nokia.com>

web: Support renaming the XSRF cookie

This makes it possible to use the __Host- cookie prefix for increased
security

docs: Point to stable branch for all demo links

Add a README to the demos directory with a brief description of each,
and a warning about the usage of not-yet-released features.

Fixes #3236

testing: No longer silence deprecation warnings

Only do it on the specific versions that had the problematic warnings.

Also deprecate get_new_ioloop.

Revert some deprecations, following asyncio changes

wsgi: Support ThreadPoolExecutor

Required making WSGIContainer.environ() an instance method.
This is technically a backwards-incompatible change to a documented
method but it was never really meant to be documented and seems
unlikely to be used.

ci: Re-enable Python 3.12 alphas

Early releases in these two branches had different deprecation warnings
so we want to test them too.

As of 3.12a5 the deprecation warnings should be in their final
state.

Also update setup-python action to silence a warning.

AsyncioLoop.start() used to save, set, and restore the thread-local
event loop. This avoided some edge cases in early versions of asyncio;
this appears to no longer be necessary since Python 3.7 introduced
the get_running_loop() method.

Removing this logic improves compatibility with Python 3.12, where
it is difficult if not impossible to do the same thing without
generating DeprecationWarnings.

web: Cookie updates