chore(script/jsx): move defineWidget into Preact API

apps/client/src/services/frontend_script_api_preact.ts

@@ -1,13 +1,34 @@
-import { Fragment, h } from "preact";
+import { Fragment, h, VNode } from "preact";
 import * as hooks from "preact/hooks";
 
 import RightPanelWidget from "../widgets/sidebar/RightPanelWidget";
 
+export interface WidgetDefinition {
+    parent: "right-pane",
+    render: () => VNode
+}
+
+export interface WidgetDefinitionWithType extends WidgetDefinition {
+    type: "react-widget"
+}
+
 export const preactAPI = Object.freeze({
     // Core
     h,
     Fragment,
 
+    /**
+     * Method that must be run for widget scripts that run on Preact, using JSX. The method just returns the same definition, reserved for future typechecking and perhaps validation purposes.
+     *
+     * @param definition the widget definition.
+     */
+    defineWidget(definition: WidgetDefinition) {
+        return {
+            type: "react-widget",
+            ...definition
+        };
+    },
+
     RightPanelWidget,
 
     ...hooks