Access let-bound parameters in component signature using :: syntax

[rachitnigam]

It would be nice and symmetrical to be able to access the let-defined parameters in a component's signature in the same way we access the some parameters:

comp Foo[N](...) with {
  some L;
  let Chunks = L / N;
} { ... }

comp main(...) {
  F := new Foo[10];
  let foo = F::Chunks;
}

This way the let parameter define a bunch of nice, generally useful parameters that callers of the module might also want to use.