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.

cypress/integration/rendering/stateDiagram.spec.js

@@ -1,4 +1,4 @@
-import { imgSnapshotTest, renderGraph } from '../../helpers/util';
+import { imgSnapshotTest, renderGraph } from '../../helpers/util.js';
 
 describe('State diagram', () => {
   it('should render a simple state diagrams', () => {