Allow for importing methods

[hubertp]

Pull Request Description

Importing individual methods didn't work as advertised because parser
would allow them but later drop that information. This slipped by because we never had mixed atoms and methods in stdlib.

Important Notes

Added some basic tests but we need to ensure that the new parser allows for this.
@jdunkerley will be adding some changes to stdlib that will be testing this functionality as well.

Checklist

Please include the following checklist in your PR:

• The documentation has been updated if necessary.
• All code conforms to the
  Scala,
  Java,
  and
  Rust
  style guides.
• All code has been tested:
  • Unit tests have been written where possible.
  • If GUI codebase was changed: Enso GUI was tested when built using BOTH
    ./run ide dist and ./run ide watch.

[jdunkerley]

LGTM but needs @4e6 review :)

[hubertp]

Figured out how to add some basic tests. This is gtg