Don't show 'unpin' for persistent widgets

This will mostly fix https://github.com/vector-im/element-web/issues/15139
although it could still break in a race condition.

src/components/views/context_menus/WidgetContextMenu.js

@@ -26,8 +26,8 @@ export default class WidgetContextMenu extends React.Component {
         // Callback for when the revoke button is clicked. Required.
         onRevokeClicked: PropTypes.func.isRequired,
 
-        // Callback for when the unpin button is clicked. Required.
-        onUnpinClicked: PropTypes.func.isRequired,
+        // Callback for when the unpin button is clicked. If absent, unpin will be hidden.
+        onUnpinClicked: PropTypes.func,
 
         // Callback for when the snapshot button is clicked. Button not shown
         // without a callback.
@@ -86,11 +86,13 @@ export default class WidgetContextMenu extends React.Component {
             );
         }
 
-        options.push(
-            <MenuItem className="mx_WidgetContextMenu_option" onClick={this.onUnpinClicked} key="unpin">
-                {_t("Unpin")}
-            </MenuItem>,
-        );
+        if (this.props.onUnpinClicked) {
+            options.push(
+                <MenuItem className="mx_WidgetContextMenu_option" onClick={this.onUnpinClicked} key="unpin">
+                    {_t("Unpin")}
+                </MenuItem>,
+            );
+        }
 
         if (this.props.onReloadClicked) {
             options.push(

src/components/views/elements/AppTile.js

@@ -841,7 +841,7 @@ export default class AppTile extends React.Component {
             contextMenu = (
                 <ContextMenu {...aboveLeftOf(elementRect, null)} onFinished={this._closeContextMenu}>
                     <WidgetContextMenu
-                        onUnpinClicked={this._onUnpinClicked}
+                        onUnpinClicked={ActiveWidgetStore.getWidgetPersistence(this.props.app.id) ? null : this._onUnpinClicked}
                         onRevokeClicked={this._onRevokeClicked}
                         onEditClicked={showEditButton ? this._onEditClick : undefined}
                         onDeleteClicked={showDeleteButton ? this._onDeleteClick : undefined}