Support node16 module resolution

The `node16` module resolution requires imports to use the `.js` file
extension in type definitions.

`@rollup/plugin-typescript` is needed to make this work with the Vite
setup used by Mermaid.

The module option for Mermaid internally is set to `nodenext`. This is
needed to support `.json` imports. Note that setting `module` to
`node16` or `nodenext` implies a matching `moduleResolution` value.

packages/mermaid-example-diagram/src/exampleDiagramRenderer.js

@@ -1,6 +1,6 @@
 /** Created by knut on 14-12-11. */
 import { select } from 'd3';
-import { log, getConfig, setupGraphViewbox } from './mermaidUtils';
+import { log, getConfig, setupGraphViewbox } from './mermaidUtils.js';
 
 /**
  * Draws a an info picture in the tag with id: id based on the graph definition in text.