docs(importmaps): use importmaps for external script

[daker]

Context

Recommend the use of importmaps

Results

Changes

• Documentation and TypeScript definitions were updated to match those changes

PR and Code Checklist

• semantic-release commit messages
• Run npm run reformat to have correctly formatted code

Testing

• This change adds or fixes unit tests
• Tested environment:
  • vtk.js:
  • OS:
  • Browser:

[finetjul]

There are other places that reference https://unpkg.com/vtk.js, you might want to modify those as well...

@floryst should we mention both options ? with and without import maps ?

[finetjul]

LGTM

[floryst]

Overall looks good. I would like to request that we add the ES module code in addition to the UMD bundle. We can have two headings, such as "Using ES Modules" and "Using the UMD bundle", in that order.