Update node.js import to make them es compatible

[Kurtil]

While testing new stuffs on the repo, I use to test examples with a web server (vscode live server) while updating the import of the xeokit sdk from dist to src. However, a lot of import are not web compatible but node.js compatible. Because of that, it is a pain to serve the examples without a bundler.

This PR aims to ensure the maximum of import are web compatible (some of theme like html2canvas needs to be processed by a bundler or commented to let the viewer start on the browser with the dev server).

[ghost]

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[Kurtil]

🎉 @xeolabs no need to comment the html2canvas import of the Viewer.js file if the browser supports importmap. I had these lines on the html head of the desired examples and it works perfectly:

    <script type="importmap">
        {
          "imports": {
            "html2canvas/dist/html2canvas.esm.js": "https://cdn.jsdelivr.net/npm/[email protected]/dist/html2canvas.esm.js"
          }
        }
    </script>

Thanks to this PR and the lines above, (+ update the import of the xeokit-sdk from dist to src), it is possible to dev on xeokit with a minimal dev environment (a dev server) ! :D