missing path2d support for freedawings, remove node-side rendering, allow async getContent()

* ## Excalidraw and SVG
 * 2022-04-16 - @thfrei
 *
 * Known issues:
 *  - excalidraw-to-svg (node.js) does not render any hand drawn (freedraw) paths. There is an issue with
 *    Path2D object not present in node-canvas library used by jsdom. (See Trilium PR for samples and other issues
 *    in respective library. Link will be added later). Related links:
 *     - https://github.com/Automattic/node-canvas/pull/2013
 *     - https://github.com/google/canvas-5-polyfill
 *     - https://github.com/Automattic/node-canvas/issues/1116
 *     - https://www.npmjs.com/package/path2d-polyfill
 *  - excalidraw-to-svg (node.js) takes quite some time to load an image (1-2s)
 *  - excalidraw-utils (browser) does render freedraw, however NOT freedraw with background
 *
 * Due to this issues, we opt to use **only excalidraw in the frontend**. Upon saving, we will also get the SVG
 * output from the live excalidraw instance. We will save this **SVG side by side the native excalidraw format
 * in the trilium note**.
 *
 * Pro: we will combat bit-rot. Showing the SVG will be very fast, since it is already rendered.
 * Con: The note will get bigger (maybe +30%?), we will generate more bandwith.
 *      (However, using trilium desktop instance, does not care too much about bandwidth. Size increase is probably
 *       acceptable, as a trade off.)

src/public/app/services/library_loader.js

@@ -67,15 +67,6 @@ const EXCALIDRAW = {
     // ]
 };
 
-const EXCALIDRAW_UTILS = {
-    /**
-     * FIXME: excalidraw-utils does not render pen-background. maybe own built required?
-     */
-    js: [
-        "node_modules/@excalidraw/utils/dist/excalidraw-utils.min.js", //v0.1.2
-    ]
-};
-
 async function requireLibrary(library) {
     if (library.css) {
         library.css.map(cssUrl => requireCss(cssUrl));
@@ -127,6 +118,5 @@ export default {
     WHEEL_ZOOM,
     FORCE_GRAPH,
     MERMAID,
-    EXCALIDRAW,
-    EXCALIDRAW_UTILS
+    EXCALIDRAW
 }