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/exampleDiagramDb.js

@@ -1,5 +1,5 @@
 /** Created by knut on 15-01-14. */
-import { log } from './mermaidUtils';
+import { log } from './mermaidUtils.js';
 
 var message = '';
 var info = false;