Implement MSC3575: Sliding Sync (#8328)

* Add labs flag for sliding sync; add sliding_sync_proxy_url to config.json

* Disable the labs toggle if sliding_sync_proxy_url is not set

* Do validation checks on the sliding sync proxy URL before enabling it in Labs

* Enable sliding sync and add SlidingSyncManager

* Get room subscriptions working

* Hijack renderSublists in sliding sync mode

* Add support for sorting alphabetically/recency and room name filters

* Filter out tombstoned rooms; start adding show more logic

list ranges update but the UI doesn't

* update the UI when the list is updated

* bugfix: make sure the list sorts numerically

* Get invites transitioning correctly

* Force enable sliding sync and labs for now

* Linting

* Disable spotlight search

* Initial cypress plugins for Sliding Sync Proxy

* Use --rm when running Synapse in Docker for Cypress tests

* Update src/MatrixClientPeg.ts

Co-authored-by: Travis Ralston <travisr@matrix.org>

* Update src/components/views/rooms/RoomSublist.tsx

Co-authored-by: Travis Ralston <travisr@matrix.org>

* Update src/settings/controllers/SlidingSyncController.ts

Co-authored-by: Travis Ralston <travisr@matrix.org>

* Update src/components/views/rooms/RoomSublist.tsx

Co-authored-by: Travis Ralston <travisr@matrix.org>

* WIP add room searching to spotlight search

* Only read sliding sync results when there is a result, else use the local cache

* Use feature_sliding_sync not slidingSync

* Some review comments

* More review comments

* Use RoomViewStore to set room subscriptions

* Comment why any

* Update src/components/views/rooms/RoomSublist.tsx

Co-authored-by: Michael Telatynski <7t3chguy@gmail.com>

* Fix cypress docker abstraction

* Iterate sliding sync proxy support

* Stash mostly functional test

* Update sliding sync proxy image

* i18n

* Add support for spaces; use list ID -> index mappings

- Mappings are more reusable and easier to understand than
  racing for index positions.
- Register for all spaces immediately on startup.

* When the active space is updated, update the list registration

* Set spaces filter in the correct place

* Skeleton placeholder whilst loading the space

* Filter out spaces from the room list

* Use the new txn_id promises

* Ensure we actually resolve list registrations

* Fix matrix-org/sliding-sync#30: don't show tombstoned search results

* Remove unused imports

* Add SYNCV3_SECRET to proxy to ensure it starts up; correct aliases for SS test

* Add another basic sliding sync e2e test

* Unbreak netlify

* Add more logging for debugging duplicate rooms

* If sliding sync is enabled, always use the rooms result even if it's empty

* Drop-in copy of RoomListStore for sliding sync

* Remove conditionals from RoomListStore - we have SlidingRoomListStore now

* WIP SlidingRoomListStore

* Add most sliding sync logic to SlidingRoomListStore

Still lots of logic in RoomSublist. Broken things:
 - Join count is wrong completely.
 - No skeleton placeholder when switching spaces.

* Migrate joined count to SS RLS

* Reinstate the skeleton UI when the list is loading

* linting

* Add support for sticky rooms based on the currently active room

* Add a bunch of passing SS E2E tests; some WIP

* Unbreak build from git merge

* Suppress unread indicators in sliding sync mode

* Add regression test for https://github.com/matrix-org/sliding-sync/issues/28

* Add invite test flows; show the invite list

The refactor to SS RLS removed the invite list entirely.

* Remove show more click as it wasn't the bug

* Linting and i18n

* only enable SS by default on netlify

* Jest fixes; merge conflict fixes; remove debug logging; use right sort enum values

* Actually fix jest tests

* Add support for favourites and low priority

* Bump sliding sync version

* Update sliding sync labs to be user configurable

* delint

* To disable SS or change proxy URL the user has to log out

* Review comments

* Linting

* Apply suggestions from code review

Co-authored-by: Travis Ralston <travisr@matrix.org>

* Update src/stores/room-list/SlidingRoomListStore.ts

Co-authored-by: Travis Ralston <travisr@matrix.org>

* Review comments

* Add issue link for TODO markers

* Linting

* Apply suggestions from code review

Co-authored-by: Michael Telatynski <7t3chguy@gmail.com>

* More review comments

* More review comments

* stricter types

Co-authored-by: Michael Telatynski <7t3chguy@gmail.com>
Co-authored-by: Travis Ralston <travisr@matrix.org>

src/i18n/strings/en_EN.json

@@ -907,6 +907,7 @@
     "Right panel stays open (defaults to room member list)": "Right panel stays open (defaults to room member list)",
     "Jump to date (adds /jumptodate and jump to date headers)": "Jump to date (adds /jumptodate and jump to date headers)",
     "Send read receipts": "Send read receipts",
+    "Sliding Sync mode (under active development, cannot be disabled)": "Sliding Sync mode (under active development, cannot be disabled)",
     "Live Location Sharing (temporary implementation: locations persist in room history)": "Live Location Sharing (temporary implementation: locations persist in room history)",
     "Favourite Messages (under active development)": "Favourite Messages (under active development)",
     "Use new session manager (under active development)": "Use new session manager (under active development)",
@@ -2856,6 +2857,14 @@
     "Link to selected message": "Link to selected message",
     "Link to room": "Link to room",
     "Command Help": "Command Help",
+    "Checking...": "Checking...",
+    "Your server has native support": "Your server has native support",
+    "Your server lacks native support": "Your server lacks native support",
+    "Your server lacks native support, you must specify a proxy": "Your server lacks native support, you must specify a proxy",
+    "Sliding Sync configuration": "Sliding Sync configuration",
+    "To disable you will need to log out and back in, use with caution!": "To disable you will need to log out and back in, use with caution!",
+    "Proxy URL (optional)": "Proxy URL (optional)",
+    "Proxy URL": "Proxy URL",
     "Sections to show": "Sections to show",
     "This groups your chats with members of this space. Turning this off will hide those chats from your view of %(spaceName)s.": "This groups your chats with members of this space. Turning this off will hide those chats from your view of %(spaceName)s.",
     "Space settings": "Space settings",