Pop out of Threads Activity Centre (#12136)

* Add `Thread Activity centre` labs flag

* Rename translation string

* WIP Thread Activity Centre

* Update supportedLevels

* css lint

* i18n lint

* Fix labs subsection test

* Update Threads Activity Centre label

* Rename Thread Activity Centre to Threads Activity Centre

* Use compound `MenuItem` instead of custom button

* Color thread icon when hovered

* Make the pop-up scrollable and add a max height

* Remove Math.random in key

* Remove unused class

* Change add comments on `mx_ThreadsActivityRows` and `mx_ThreadsActivityRow`

* Make threads activity centre labs flag split out unread counts

Just shows notif & unread counts for main thread if the TAC is enabled.

* Fix tests

* Simpler fix

* Open thread panel when thread clicke in Threads Activity Centre

Hopefully this is a sensible enough way. The panel will stay open of
course (ie. if you go to a different room & come back), but that's the
nature of the right panel.

* Dynamic state of room

* Add doc

* Use the StatelessNotificationBadge component in ThreadsActivityCentre

and re-use the existing NotificationLevel

* Remove unused style

* Add room sorting

* Fix `ThreadsActivityRow` props doc

* Pass in & cache the status of the TAC labs flag

* Pass includeThreads as setting to doesRoomHaveUnreadMessages too

* Fix tests

* Add analytics to the TAC (#12179)

* Update TAC label (#12186)

* Add `IndicatorIcon` to the TAC button (#12182)

Add `IndicatorIcon` to the TAC button

* Threads don't have activity if the room is muted

This makes it match the computation in determineUnreadState.
Ideally this logic should all be in one place.

* Re-use doesRoomHaveUnreadThreads for useRoomThreadNotifications

This incorporates the logic of not showing unread dots if the room
is muted

* Add TAC description in labs (#12197)

* Fox position & size of dot on the tac button

IndicatorIcon doesn't like having the size of its icon adjusted and
we probably shouldn't do it anyway: better to specify to the component
what size we want it.

* TAC: Utils tests (#12200)

* Add tests for `doesRoomHaveUnreadThreads`
* Add tests for `getThreadNotificationLevel`

* Add test for the ThreadsActivityCentre component

* Add snapshot test

* Fix narrow hover background on TAC button

Make the button 32x32 (and the inner icon 24x24)

* Add caption for empty TAC

* s/tac/threads_activity_centre/

* Fix i18n & add tests

* Add playwright tests for the TAC (#12227)

* Fox comments

---------

Co-authored-by: David Baker <dbkr@users.noreply.github.com>

res/css/structures/_ThreadsActivityCentre.pcss

@@ -0,0 +1,74 @@
+/*
+ *
+ * Copyright 2024 The Matrix.org Foundation C.I.C.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ * /
+ */
+
+.mx_ThreadsActivityCentreButton {
+    color: $secondary-content;
+    height: 32px;
+    width: 32px;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    border-radius: 8px;
+    margin: auto;
+
+    &.expanded {
+        /* align with settings icon */
+        margin-left: 20px;
+
+        & > .mx_ThreadsActivityCentreButton_IndicatorIcon {
+            /* align with settings label */
+            margin-right: 12px;
+        }
+    }
+
+    &:not(.expanded) {
+        &:hover,
+        &:hover .mx_ThreadsActivityCentreButton_Icon {
+            background-color: $quaternary-content;
+            color: $primary-content;
+        }
+    }
+
+    & .mx_ThreadsActivityCentreButton_Icon {
+        color: $secondary-content;
+    }
+}
+
+.mx_ThreadsActivity_rows {
+    overflow-y: scroll;
+    /* Let some space at the top and the bottom of the pop-up */
+    max-height: calc(100vh - 200px);
+
+    .mx_ThreadsActivityRow {
+        height: 48px;
+
+        /* Make the label of the MenuItem stay on one line and truncate with ellipsis if needed */
+        & > span {
+            white-space: nowrap;
+            overflow: hidden;
+            text-overflow: ellipsis;
+            width: 210px;
+        }
+    }
+}
+
+.mx_ThreadsActivityCentre_emptyCaption {
+    padding-left: 16px;
+    padding-right: 16px;
+    font-size: 13px;
+}