deduplicate definition of "function" regex, to eliminate duplication of knowledge

[uladkasach]

currently, we define regex to extract content from a function in two places:

• extractTypeDefForSelectExpressions (query)
• extractTypeDefForInputVariables (query)

so every time we modify what a valid function looks like, we have to modify in both places.

if this occurs regularly or we add a third place where we need this knowledge, we absolutely should generalize that information out into a "getFunctionDefinitionFromSql" utility - which can expose the array of arguments and the function name, satisfying all of our use cases