Do not render in-chat key verification requests in the timeline

A m.key.verification.request sent from a client that supports in-chat
verification carries a plain text body for clients that do not. Element X
has no msgtype of its own for it, so it fell through to OtherMessageType
and the timeline printed that body, telling the user their client does
not support in-chat key verification right after a verification they had
just completed.

Drop the event when building the timeline items, as Element X iOS does.

libraries/matrix/api/src/main/kotlin/io/element/android/libraries/matrix/api/timeline/item/event/MessageType.kt

@@ -128,4 +128,11 @@ sealed interface GalleryItemType {
 data class OtherMessageType(
     val msgType: String,
     val body: String,
-) : MessageType
+) : MessageType {
+    /**
+     * A `m.key.verification.request` carries a body meant for clients that cannot handle in-chat
+     * verification, so it must not be rendered as a message.
+     */
+    val isKeyVerificationRequest: Boolean
+        get() = msgType == "m.key.verification.request"
+}