A11y: improve accessibility of pinned messages (#30558)

* fix: improve aria role and label on pinned message banner

* fix: change pinned message badge background for contrast

* fix: link pinned message button to content

* test: update tests

* fix: add aria-describedby on pinned message badge

* feat: use `aria-describedby` instead of `aria-description`

* test: update room view snapshot

* test: update snapshot

* fix: put id only textual body upper div

* fix: use lodash uniqueId

* test: update snapshots

res/css/views/messages/_PinnedMessageBadge.pcss

@@ -13,7 +13,7 @@
 
     padding: var(--cpd-space-1x) var(--cpd-space-3x) var(--cpd-space-1x) var(--cpd-space-1x);
     font: var(--cpd-font-body-xs-medium);
-    background-color: var(--cpd-color-alpha-gray-200);
+    background-color: var(--cpd-color-bg-subtle-secondary);
     color: var(--cpd-color-text-secondary);
 
     border-radius: 99px;