support CPS transformations on nnkLambda and non-top-level procs

[zevv]

Could we support this?

let foo = proc() {.cps:C.} =  
  echo "foo"  
foo()  

And if possible, even this?

proc foo() {.cps:C.} = 
                      
  proc bar() {.cps:C.} = 
    echo "bar"          
                           
  bar()        
                      
foo()

and this

proc foo() {.cps:C.} = 
  let bar = proc() {.cps:C.} =
    echo "bar"           
  bar()                 
foo()  

[disruptek]

let foo = proc() {.cps:C.} =  
  echo "foo"  
foo()

I don't see how we can support this as long as the compiler rejects the following:

let foo =
  type C = ref object of Continuation
  proc(): C = echo "foo"

And unfortunately, unless we add an untyped pass, this means we cannot support the last example.

But the 2nd example, sure, we should be able to support that.