Fix documentation build by replacing removed --polyglot flag

[afarber]

Issue

Fixes #7274

The --polyglot flag was removed from documentation.js in 2017. When OSRM upgraded to v14 in PR #7141, this went unnoticed because documentation.js silently ignores unknown arguments (exits 0 after printing help).

This PR adds a simple script to extract JSDoc comments from the C++ file and feed them to documentation.js, replacing the old --polyglot functionality.

Note: The docbox HTML build (the second part of npm run docs) also fails due to ESM/CommonJS conflicts introduced when the project switched to "type": "module". That's tracked separately in the issue #7293.

Tasklist

• [x] CHANGELOG.md entry (How to write a changelog entry)
• [ ] update relevant Wiki pages
• [ ] add tests (see testing documentation)
• [ ] review
• [ ] adjust for comments