text: Title: Add typing to all modules under `robot.api`
  Body: Currently, the `@keyword` and `@library` functions exposed through the `robot.api` module have no annotations. This limits the type-checking that tools like mypy and Pylance / pyright can perform, in turn limiting what types of issues language servers can detect.
  
  Adding annotations to these functions (and, ultimately, all public-facing interfaces of the Robot Framework) would enable better IDE / tool integration.
  
  Note that the improvements with regards to automatic type conversion also closely relate to this issue since the framework uses the signatures of methods decorated with the `@keyword` decorator to attempt automatic type conversion, while the missing annotations limit static analysis of the decorated methods.