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/widgets/note_detail.js

@@ -68,7 +68,7 @@ export default class NoteDetailWidget extends NoteContextAwareWidget {
             const {noteId} = note;
 
             const dto = note.dto;
-            dto.content = this.getTypeWidget().getContent();
+            dto.content = await this.getTypeWidget().getContent();
 
             // for read only notes
             if (dto.content === undefined) {