Convert markdown to HTML when a caption is edited

Adding or editing a media caption from the plain composer sent the
caption as text only: the composer has no HTML to pass, and the media
caption edit was built by hand with a null formatted body, so the
markdown was never rendered. Sending a caption with the same markdown
does render it, because the SDK builds the formatted body there.

Build the edit with the SDK's createCaptionEdit, which runs the caption
through the same markdown conversion the send path uses.

libraries/matrix/impl/src/main/kotlin/io/element/android/libraries/matrix/impl/timeline/RustTimeline.kt

@@ -75,6 +75,7 @@ import org.matrix.rustcomponents.sdk.PollData
 import org.matrix.rustcomponents.sdk.SendAttachmentJoinHandle
 import org.matrix.rustcomponents.sdk.UploadParameters
 import org.matrix.rustcomponents.sdk.UploadSource
+import org.matrix.rustcomponents.sdk.createCaptionEdit
 import org.matrix.rustcomponents.sdk.use
 import timber.log.Timber
 import uniffi.matrix_sdk.PaginationStatus
@@ -341,7 +342,7 @@ class RustTimeline(
         formattedCaption: String?,
     ): Result<Unit> = withContext(dispatcher) {
         runCatchingExceptions<Unit> {
-            val editedContent = EditedContent.MediaCaption(
+            val editedContent = createCaptionEdit(
                 caption = caption,
                 formattedCaption = formattedCaption?.let {
                     FormattedBody(body = it, format = MessageFormat.Html)