Add workbench.build experimental API (#690)

Author: sonnyp

src/Previewer/Internal.js

@@ -5,6 +5,7 @@ import GObject from "gi://GObject";
 import Adw from "gi://Adw";
 
 import { once } from "../../troll/src/async.js";
+import { build } from "../../troll/src/builder.js";
 
 // eslint-disable-next-line no-restricted-globals
 const { addSignalMethods } = imports.signals;
@@ -80,6 +81,10 @@ export default function Internal({
         dropdown_preview_align.selected = 0;
         preview(object);
       },
+      build(params) {
+        console.warn("workbench.build is experimental");
+        return build(panel_ui.xml, params);
+      },
     };
 
     let obj;