Render Diviner atom signatures on one line

Summary:
Ref T988. Instead of rendering this:

  ClassName
  final class ClassName

  methodName
  final public function methodName(...)

...just render this:

  final class ClassName

  final public function methodName(...)

Also link and anchor the method names.

Test Plan:
Before:

{F57536}
{F57537}

After:

{F57538}
{F57539}

Reviewers: chad

Reviewed By: chad

CC: aran

Maniphest Tasks: T988

Differential Revision: https://secure.phabricator.com/D6908