JS functions do not round trip through Generator templates

[cmars]

RE: loadFunctions, if you pass a Go value to a JS function and return it, it's likely that the generator template will be unable to access it's fields and methods.

The resulting object seems to be a goja.Object.

Options:

• Wrap goja-dispatched functions with something that can unwrap an underlying type. If that's possible
• Wrap goja return values with something that text/template can process (a map[string]interface{} maybe?)
• Don't do anything, just document the behavior.

CC @mrded

[jcsackett]

Given the funcmap being added, do we want to just document the behavior for js functions now? And maybe in said documentation recommend when to use which?

[cmars]

Sounds good to me!