TypeOf and support for JSON Schema generation for functions

[vazirim]

Is your feature request related to a problem? Please describe.
During tool calling, it's useful to define a PDL function that can then be passed as one of the available tools. Today the user has to write the JSON schema corresponding to the PDL function manually. It would be good to automate this.

Describe the solution you'd like
A typeOf() function on any variable will allow users to define a function, assign it to a variable, and obtain its JSON Schema automatically.

For function signatures we also need descriptions. So we need more than typeOf for the tool calling use case.

Describe alternatives you've considered
N/A

Additional context

This issue was inspired by a suggestion from @eloycoto.

[vazirim]

@mandel we need to figure out how to obtain descriptions for the signatures as well.
In addition to typeof, you had also suggested a way to add consumable comments to function definitions. Could you please document that here?

[eloycoto]

Also function args, in tools we need: type, description and sometimes enums