follow up patch to fn :decorators support, minor doc and test update

[ikappaki]

Hi,

can you please consider the follow up patch for anonymous fn decorators support (#1189).

• Moved the note in python interop decorators doc at the top, as it contains important policy information.
• Updated the fn docstring to document the form/name metadata precedence rules established in Adds support for :decorators in anon fns, defasync #1189, where name metadata takes precedence over form.
• Added new test to verify precedence rule.
• Corrected a test that was mistakenly using defn instead of fn.

I don't think this requires a changelog entry but I can add if necessary.

Thanks