Check appservice user interest against the local users instead of all users (`get_users_in_room` mis-use)

[MadLittleMods]

Check appservice user interest against the local users instead of all users (get_users_in_room mis-use).

get_local_users_in_room is way more performant since it looks at a single table (local_current_membership) and is looking through way less data since it only worries about the local users in the room instead of everyone in the room across the federation.

Fix https://github.com/matrix-org/synapse/issues/13942 (probably fixes, we don't know for sure but it's our hunch atm)

Related to https://github.com/matrix-org/matrix-spec/issues/1272

Related to the following PRs where we also cleaned up some get_users_in_room mis-uses:

• https://github.com/matrix-org/synapse/pull/13605
• https://github.com/matrix-org/synapse/pull/13608
• https://github.com/matrix-org/synapse/pull/13606
• https://github.com/matrix-org/synapse/pull/13960

See https://github.com/matrix-org/synapse/pull/13575#discussion_r953023755 for the original exploration around finding get_users_in_room mis-uses.

Problem

https://github.com/matrix-org/synapse/pull/13575 made the get_users_in_room SQL query a little more complicated by adding an extra join statement to the query which means it takes more time.

This extra database time can show up as a hot-spot for homeservers that make heavy use of application services and bridged users (like Element One), see https://github.com/matrix-org/synapse/issues/13942

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[MadLittleMods]

Thanks for the review @squahtx, @clokep, and @anoadragon453 🐎

[MadLittleMods]

Thanks for the review @squahtx, @clokep, @anoadragon453, and @turt2live 🦨