Backend for listing instantiations of primitives

[ayakayorihiro]

This PR contains a new backend that lists all of the unique instantiations of primitives within a program into a JSON file. This is necessary for my Calyx-FIRRTL efforts because FIRRTL does not support parameterization of modules, and therefore I have to generate individual FIRRTL modules that each correspond to a specific primitive instantiation in Calyx. This backend is the first step, and the produced JSON file will be processed by a script that I will write next. I'll also add fud2 support for this backend soon.
As a side note, this backend would also be similarly useful for the BTOR2-Cider efforts as described in #1845 under Generation Scaffolding.

This backend borrowed a lot of code from the Resource Estimation backend, which I'm very thankful for 🙂

Please let me know if there's any points I can improve here!! Also, I'm personally not a fan of the namings I used (primitive-inst, primtives.rs, etc) but didn't have any better ideas, so I'd really appreciate any suggestions on that front 🙂

Usage

You can run the backend by using the -b primitive-inst flag, and the optional -o <OUTPUT_FILE> flag to write the JSON to a file.

ex) Running with language-tutorial-mem:

cargo run -- examples/tutorial/language-tutorial-mem.futil -b primitive-inst -o p.json

we get in p.json...

[
  {
    "name": "std_mem_d1",
    "params": [
      {
        "param_name": "WIDTH",
        "param_value": 32
      },
      {
        "param_name": "SIZE",
        "param_value": 1
      },
      {
        "param_name": "IDX_SIZE",
        "param_value": 1
      }
    ]
  }
]

[sampsyo]

Heck yes!!! This seems perfect! Wahoo! Just have a couple of code-level suggestions within.

As for the name, maybe something like primitive-uses or primitives-used something would be nice and clear? We could even call the source file primitive_uses.rs.

[sampsyo]

Not that this matters very much, but this is probably possible to write in a functional way (and eliminate mut, in favor of collect). I think it would look something like this (although I haven't tested it):

let curr_params: Vec<_> = param_binding.iter().map(|param_name, param_size| {
  PrimitiveParam {
    // unchanged
  }
}).collect();

[ayakayorihiro]

This is super cool! Thanks for the suggestion :)

[sampsyo]

Wonderful; looks great! Merge at will, I say. 😃

[EclecticGriffin]

Looks good to me, left a few minor notes that you can take or leave

[EclecticGriffin]

There is a method on Context called entrypoint which does this exact thing.
It's functionally the same but might as well make use of it

[EclecticGriffin]

This is a more idiomatic way of writing it. Better when you might want to use
something as more than a mutable reference down the line

Suggested change

	gen_primitive_set(ctx, main_comp, primitive_set);
	let mut primitive_set: HashSet<PrimitiveUse> = HashSet::new();
	gen_primitive_set(ctx, main_comp, &mut primitive_set);