Function isAsyncFunction

Checks if value is declared as an AsyncFunction. This includes only async () => Promise<any> declarations, but NOT normal functions that returns a Promise (i.e () => Promise<any>).

It includes only 'asyncNormalFunction', 'a_Function_Async_normalAnonymous', 'a_Function_async_arrow_named', 'a_Function_async_arrow_anonymous' and it excludes 'a_GeneratorFunction_async_named' & 'a_GeneratorFunction_async_anonymous' and all others.