codegen: Handle 'secret(..)' functions

[abhinav]

Hello!

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Issue details

Follow-up to: #487 (comment)

Specifically, in gen_program.go, genResource has special handling for "secret"
separately from generator.function which doesn't recognize the "secret"
function.

This code was also previously tracking the arguments to the secret function
but not doing anything with that information.
This unused slice was dropped in #487.

This issue tracks the follow-up of that.

Affected area/feature

codegen