Add API for all built-in expresssion functions

From the SQL functions documentation:

Commonly used functions available for DataFrame operations. Using functions defined here provides a little bit more compile-time safety to make sure the function exists.

Functions such as "inline_outer" are actually commonly used, but are not currently included in the API, meaning that we lose compile-time safety for those invocations. We should implement the required function definitions for the remaining built-in functions when applicable.