Add support for MD / HTML in room topics (#8215)

* Add support for MD / HTML in room topics

Setting MD / HTML supported:
- /topic command
- Room settings overlay
- Space settings overlay

Display of MD / HTML supported:
- /topic command
- Room header
- Space home

Based on extensible events as defined in [MSC1767]

Fixes: vector-im/element-web#5180
Signed-off-by: Johannes Marbach <johannesm@element.io>

[MSC1767]: matrix-org/matrix-spec-proposals#1767

* Fix build error

* Add comment to explain origin of styles

Co-authored-by: Travis Ralston <travpc@gmail.com>

* Empty commit to retrigger build

* Fix import grouping

* Fix useTopic test

* Add tests for HtmlUtils

* Add slash command test

* Add further serialize test

* Fix ternary formatting

Co-authored-by: Travis Ralston <travpc@gmail.com>

* Add blank line

Co-authored-by: Travis Ralston <travpc@gmail.com>

* Properly mock SettingsStore access

* Remove trailing space

* Assert on HTML content and add test for plain text in HTML parameter

* Appease the linter

* Fix JSDoc comment

* Fix toEqual call formatting

* Repurpose test for literal HTML case

* Empty commit to fix CI

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

res/css/views/rooms/_RoomHeader.scss

@@ -166,6 +166,12 @@ limitations under the License.
     display: -webkit-box;
 }
 
+.mx_RoomHeader_topic .mx_Emoji {
+    // Undo font size increase to prevent vertical cropping and ensure the same size
+    // as in plain text emojis
+    font-size: inherit;
+}
+
 .mx_RoomHeader_avatar {
     flex: 0;
     margin: 0 6px 0 7px;