tsp - Add description for array body and path parameter if missing

[dolauli]

This pull request improves how parameter and array schema descriptions are generated in the TypeSpec PowerShell converter, leading to more informative and user-friendly documentation output. The main changes focus on enhancing the fallback logic for descriptions when explicit documentation is missing.

Improvements to description generation:

• In convertor.ts, the logic for creating a parameter description now falls back to the schema's description if explicit documentation is unavailable, ensuring that parameters always have a meaningful description.
• In modelUtils.ts, array schema descriptions now use available documentation or, if missing, generate a description like "Array of [type name]", making array types clearer in generated docs.