[FIX] Docs: enforce file extensions for ES6 import specifiers.

[thibsy]

Hi folks,

Technically, it is not possible to create JavaScript bundles using Rollup.js right now, because our code-style disallows file extensions in ES6 import specifiers, but the module bundler requires them. This is due to the Node.js specification of import specifiers, which states that a file extension is always necessary for relative specifiers. Since we are maintaining a repository and cannot use absolute specifiers, we need to make a code-style adjustment.

This PR therefore changes:

• the ESLint configuration to enforce file extensions in import statements, except for specifiers that are resolved by other tools like Node.js itself or Rollup.js
• the JavaScript code-style to document why the change is necessary

Kind regards,
@thibsy

[matthiaskunkel]

Jour Fixe, 06 JAN 2025: Thibeau notified us about this change in the JavaScript handling for 10 and trunk.