Add function tests for new features

[jnasbyupgrade]

From what I can tell, pgTap is currently lacking support for testing the following attributes of a function:

• transform for type
• leakproof
• parallel safe
• cost
• rows
• support function
• function settings (Add support for testing options/properties on an object #351)

I'm opening this issue as a means to track these. I do intend to at least add leakproof and parallel safe, and probably #351, since I currently have need of those. I can look at the others as well.

Of course if someone wants to beat me to this, have at it! 😆