Temporarily revert "Add functionality to remove deactivated users from the monthly_active_users table (#10947)".

This reverts commit eda8c88b.

Signed-off-by: Dan Callahan <danc@element.io>

The following scenarios would halt the user directory updater:

- user joins room
- user leaves room
- user present in room which switches from private to public, or vice versa.

for two classes of users:

- appservice senders
- users missing from the user table.

If this happened, the user directory would be stuck, unable to make forward progress.

Exclude both cases from the user directory, so that we ignore them.

Co-authored-by: Eric Eastwood <erice@element.io>
Co-authored-by: reivilibre <oliverw@matrix.org>
Co-authored-by: Sean Quah <8349537+squahtx@users.noreply.github.com>
Co-authored-by: Brendan Abolivier <babolivier@matrix.org>

The race allowed the current position to advance too far when stream IDs
are still being persisted.

This happened when it received a new stream ID from a remote write
between a new stream ID being allocated and it being added to the set of
unpersisted stream IDs.

Fixes #9424.

This reverts #11019 and structures the code a bit more like it was before #10985.

The global cache state must be reset before running the tests since other test
cases might have configured caching (and thus touched the global state).

Pass through `SynapseError`s that are raised from experimental `check_event_allowed` callback of the module API (#11042)

Co-authored-by: Brendan Abolivier <babolivier@matrix.org>

Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>

Searches the returned HTML for an oEmbed endpoint using the
autodiscovery mechanism (`<link rel=...>`), and will request it
to generate the preview.

Signed-off-by: Olivier Wilkinson (reivilibre) <oliverw@matrix.org>

Also mark `synapse.streams` as having has no untyped defs

Co-authored-by: Sean Quah <8349537+squahtx@users.noreply.github.com>

Updating mypy past version 0.9 means that third-party stubs are no-longer distributed with typeshed. See http://mypy-lang.blogspot.com/2021/06/mypy-0900-released.html

 for details.
We therefore pull in stub packages in setup.py

Additionally, some modules that we were previously ignoring import failures for now have stubs. So let's use them.

The rest of this change consists of fixups to make the newer mypy + stubs pass CI.

Co-authored-by: Patrick Cloke <clokep@users.noreply.github.com>

This splits apart `handle_new_user` into a function which adds an entry to the `user_directory` and a function which updates the room sharing tables. I plan to continue doing more of this kind of refactoring to clarify the implementation.

The shared ratelimit function was replaced with a dedicated
RequestRatelimiter class (accessible from the HomeServer
object).

Other properties were copied to each sub-class that inherited
from BaseHandler.

Use `PreserveLoggingContext()` to ensure that logging contexts are not
lost when exiting a read/write lock.

When exiting a read/write lock, callbacks on a `Deferred` are triggered
as a signal to any waiting coroutines. Any waiting coroutine that
becomes runnable is likely to follow the Synapse logging context rules
and will restore its own logging context, then either run to completion
or await another `Deferred`, resetting the logging context in the
process.

This also turns off calculating code coverage, as we didn't use it and it was a lot of noise