Update prop type & documentation for HistoryVisibleBanner and VM. (#31545)

* docs: Update documentation for HistoryVisibleBanner and VM.

* docs: Improve documentation for `HistoryVisibleBanner`, second pass.

* docs: Move documentation to prop types over FC.

Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>

* fix: Simplify type for `HistoryVisibleBannerViewModel` `threadId`.

* docs: Apply suggestions from code review

Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>

---------

Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>

src/components/views/composer/HistoryVisibleBanner.tsx

@@ -11,7 +11,17 @@ import { type Room } from "matrix-js-sdk/src/matrix";
 
 import { HistoryVisibleBannerViewModel } from "../../../viewmodels/composer/HistoryVisibleBannerViewModel";
 
-export const HistoryVisibleBanner: React.FC<{ room: Room; threadId?: string | null }> = (props) => {
+/** Wrapper around {@link HistoryVisibleBannerViewModel} for the creation of an auto-disposed view model. */
+export const HistoryVisibleBanner: React.FC<{
+    /** The room instance associated with this banner view model. */
+    room: Room;
+
+    /**
+     * If not null, specifies the ID of the thread currently being viewed in the thread timeline side view,
+     * where the banner view is displayed as a child of the message composer.
+     */
+    threadId: string | null;
+}> = (props) => {
     const vm = useCreateAutoDisposedViewModel(() => new HistoryVisibleBannerViewModel(props));
     return <HistoryVisibleBannerView vm={vm} />;
 };

src/components/views/rooms/MessageComposer.tsx

@@ -675,7 +675,7 @@ export class MessageComposer extends React.Component<IProps, IState> {
 
         return (
             <div className={classes} ref={this.ref} role="region" aria-label={_t("a11y|message_composer")}>
-                <HistoryVisibleBanner room={this.props.room} threadId={threadId} />
+                <HistoryVisibleBanner room={this.props.room} threadId={threadId ?? null} />
                 <div className="mx_MessageComposer_wrapper">
                     <UserIdentityWarning room={this.props.room} key={this.props.room.roomId} />
                     <ReplyPreview