chore: move project to ESM

[csouchet]

Instruct Node.js to consider .js file as ESM module.

The package.json file has its type set to "module" and it declares "exports". This can be useful when testing code using bpmn-visualization in a Node.js environment (for instance, bv-experimental-add-ons).
It's also marked as having no side effects ("sideEffects": false) to enable tools like webpack to better manage tree shaking.

Migrate configuration files to ESM. When possible, add typings to ease configuration change in IDE.

• Configure tools to manage all specific JS/TS extensions.
• The eslint configuration file is still using CommonJS because v8.48.0 doesn't support ESM. Add typings to ease configuration change in IDE.
• jest configurations: they have not been migrated to ESM as it would require too much changes in custom setup scripts. This can be done later
• postcss configuration still using CommonJS as the documentation only mention this "flavor"

Notes

This has been detected as mandatory to run Jest tests in a ESM context. See process-analytics/bpmn-visualization-addons#95 and process-analytics/bpmn-visualization-addons#96 for more details.

Resources

Side effects free:

• webpack
  • https://webpack.js.org/blog/2020-10-10-webpack-5-release/#side-effect-analysis
  • https://webpack.js.org/guides/tree-shaking/#mark-the-file-as-side-effect-free
• same kind of mechanisms in rollup: https://rollupjs.org/guide/en/#tree-shaking
• examples in other projects: Add sideEffects: false to package.json.  d3/d3#3131, "sideEffects" annotation in package.json may be out of date tensorflow/tfjs#4248 (configure some sideEffects)

Configuration of the tools

• https://eslint.org/docs/latest/use/configure/configuration-files#configuration-file-formats
• https://jestjs.io/fr/docs/configuration
• https://github.com/postcss/postcss/blob/8.4.29/README.md
• https://prettier.io/docs/en/configuration.html
• https://tailwindcss.com/docs/configuration

Resources about exports in package.json

• exports properties checklist
  • https://docs.skypack.dev/package-authors/package-checks#check-your-score-before-publishing
  • https://docs.skypack.dev/package-authors/package-checks#export-map
• verify exports properties: https://github.com/skypackjs/package-check-action

See also process-analytics/bpmn-visualization-addons#99

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[sonarqubecloud]

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[tbouffard]

LGTM