Make trailing : into a setting (#6711)

* Make trailing `:` into a setting

Signed-off-by: Šimon Brandner <simon.bra.ag@gmail.com>

* Make traling comma opt-out

Signed-off-by: Šimon Brandner <simon.bra.ag@gmail.com>

* Write `insertTrailingComma` when reading for future opt-in setting

Signed-off-by: Šimon Brandner <simon.bra.ag@gmail.com>

* Update src/editor/parts.ts

* Fix line length

Signed-off-by: Šimon Brandner <simon.bra.ag@gmail.com>

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

src/settings/Settings.tsx

@@ -429,6 +429,11 @@ export const SETTINGS: {[setting: string]: ISetting} = {
         default: true,
         controller: new UIFeatureController(UIFeature.Widgets, false),
     },
+    "MessageComposerInput.insertTrailingComma": {
+        supportedLevels: LEVELS_ACCOUNT_SETTINGS,
+        displayName: _td('Insert a trailing colon after user mentions at the start of a message'),
+        default: true,
+    },
     // TODO: Wire up appropriately to UI (FTUE notifications)
     "Notifications.alwaysShowBadgeCounts": {
         supportedLevels: LEVELS_ROOM_OR_ACCOUNT,