Add tips for using async on Windows on Python 3.8

Bumps [pre-commit](https://github.com/pre-commit/pre-commit) from 2.12.0 to 2.12.1.
- [Release notes](https://github.com/pre-commit/pre-commit/releases)
- [Changelog](https://github.com/pre-commit/pre-commit/blob/master/CHANGELOG.md)
- [Commits](https://github.com/pre-commit/pre-commit/compare/v2.12.0...v2.12.1)
Signed-off-by: Ndependabot[bot] <support@github.com>

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Allow using Click 7 with a DeprecationWarning

Move get_root_path back to flask.helpers

As long as popular libraries (e.g. Celery) require click 7, depending
on Click 8 in Flask makes it hard to test the latest version (and its
other dependencies) in existing applications.

Many libraries use it so the move is somewhat disruptive.

[pre-commit.ci] pre-commit autoupdate

updates:
- [github.com/asottile/pyupgrade: v2.12.0 → v2.13.0](https://github.com/asottile/pyupgrade/compare/v2.12.0...v2.13.0)
- [github.com/asottile/reorder_python_imports: v2.4.0 → v2.5.0](https://github.com/asottile/reorder_python_imports/compare/v2.4.0...v2.5.0)
- [github.com/psf/black: 20.8b1 → 21.4b0](https://github.com/psf/black/compare/20.8b1...21.4b0)

This should make it easier for users to correctly use Flask. The hints
are from Quart.

This enables type checking in CI and marks the project as typed.

This has been an early question from users, so best to explain.

Whilst it has been possible to serve via an ASGI server for a while
(using WSGI to ASGI middleware/adapters) it hasn't added much. Now
though it makes sense to recommend the asgiref adapter as it
integrates with the same event loop used for async route handlers
etc...

Release 2.0.0rc1

Fix wrapped view function comparison

Wrapped functions are not comparable, see
https://bugs.python.org/issue3564, therefore a marker is used to note
when the function has been sync wrapped to allow comparison with the
wrapped function instead.

This ensures that multiple route decorators work without raising
exceptions i.e.,

    @app.route("/")
    @app.route("/a")
    async def index():
        ...

works.

deprecate `helpers.total_seconds`

locked_cached_property subclasses Werkzeug's cached_property

shell calls sys.__interativehook__

This will set up readline tab and history completion by default.

Nested blueprints

This allows blueprints to be nested within blueprints via a new
Blueprint.register_blueprint method. This should provide a use case
that has been desired for the past ~10 years.

This works by setting the endpoint name to be the blueprint names,
from parent to child delimeted by "." and then iterating over the
blueprint names in reverse order in the app (from most specific to
most general). This means that the expectation of nesting a blueprint
within a nested blueprint is met.

Bugfix iscoroutinefunction with Python3.7