Move last seen info into devices table

Enable cleaning up extremities with dummy events by default to prevent undue build up of forward extremities. (#5884)

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

Fixes #6103

If email or msisdn verification aren't supported, let's stop advertising them
for registration.

Fixes #6100.

Pull the checkers out to their own classes, rather than having them lost in a
massive 1000-line class which does everything.

This is also preparation for some more intelligent advertising of flows, as per #6100

because, frankly, it looked like it was written by an axe-murderer.

This should be a non-functional change, except that where `m.login.dummy` was
previously advertised *before* `m.login.terms`, it will now be advertised
afterwards. AFAICT that should have no effect, and will be more consistent with
the flows that involve passing a 3pid.

Fix the return value in the users_set_deactivated_flag background job

Update the process for mapping SAML2 users to matrix IDs

Added in #5377, apparently in error

Fix a bug with saml attribute maps.

Second part of solving #6076
Fixes #6076

We return a submit_url parameter on calls to POST */msisdn/requestToken so that clients know where to submit token information to.

Add a m.separate_add_and_bind flag set to True. See MSC2290's Backward Compatibility section for details.

Make the sample saml config closer to our standards

Uses a SimpleHttpClient instance equipped with the federation_ip_range_blacklist list for requests to identity servers provided by user input. Does not use a blacklist when contacting identity servers specified by account_threepid_delegates. The homeserver trusts the latter and we don't want to prevent homeserver admins from specifying delegates that are on internal IP addresses.

Fixes #5935

Adds a flag to /versions' unstable_features section indicating that this Synapse understands what an id_access_token is, as per MSC2264.

Fixes #5927

As MSC2263 states, m.require_identity_server must be set to false when it does not require an identity server to be provided by the client for the purposes of email registration or password reset.

Adds an m.require_identity_server flag to /versionss unstable_flags section. This will advertise that Synapse no longer needs id_server as a parameter.

First part of solving #6076

This is a) simpler than querying user_ips directly and b) means we can
purge older entries from user_ips without losing the required info.

The storage functions now no longer return the access_token, since it
was unused.

This allows us to purge old user_ips entries without having to preserve
the latest last seen info for active devices.

Implements MSC2290. This PR adds two new endpoints, /unstable/account/3pid/add and /unstable/account/3pid/bind. Depending on the progress of that MSC the unstable prefix may go away.

This PR also removes the blacklist on some 3PID tests which occurs in #6042, as the corresponding Sytest PR changes them to use the new endpoints.

Finally, it also modifies the account deactivation code such that it doesn't just try to deactivate 3PIDs that were bound to the user's account, but any 3PIDs that were bound through the homeserver on that user's account.

Fixes #6066

This register endpoint should be disabled if registration is disabled, otherwise we're giving anyone the ability to check if a username exists on a server when we don't need to be.

Error code is 403 (Forbidden) as that's the same returned by /register when registration is disabled.

In ancient times Synapse would only send emails when it was notifying a user about a message they received...

Now it can do all sorts of neat things!

Change the logging so it's not just about notifications.

Fix exception when resetting retry timings