feat: stdlib implementation

[wolfv]

For compatibility with recent conda-forge efforts we're implementing the stdlib jinja function.

Open questions:

• should there be any default values?
• compiler and stdlib currently evaluate to an intermediate form. Should we keep that?
• If we decide for the intermediate form, we should allow the function only in specific sections such as:
  • requirements.*
  • ignore_run_exports / from_package
• And then we should also disallow it in the test section and only allow the compiler-c or compiler-cxx packages in the test section.