feat: add new get_script_hash kernel procedure

[tomyrd]

closes #977

This PR adds a new get_script_hash kernel procedure that allows the user to access the note script hash from within the script itself.

[tomyrd]

Some documentation is still missing but I just wanted to check if my approach was correct. It's a simple procedure but I'm not so experienced in this part of the codebase, so I created this draft first. I used the get_serial_number procedure as an example for the procedures+tests.

cc @igamigo @bobbinth @Fumuran

[Fumuran]

Looks good, thank you!

I have just one comment about the test, but the assembly code for now looks good for me.

[Fumuran]

You said that you used the test for the get_serial_number as a reference, but it turned out that this test has some flaws in it. Your test (and get_serial_number one) could be rewritten like so:

    use.kernel::prologue
    use.miden::note
    begin
        exec.prologue::prepare_transaction
        exec.note::get_note_script_hash

        # truncate the stack
        swapw dropw
    end

So there are three comments:

1. As far as I know, we should avoid using procedures from the kernel lib directly, so in that case we should use the get_note_script_hash procedure from the miden lib, and not from the kernel.
2. We don't need to import the same module with different names. Probably at first there were both miden::note and kernel::note modules, that's why we wanted to have kernel::note as an internal one, but for now it is unnecessary.
3. We don't need to call note::prepare_note procedure — it just moves some data on the stack, without updating any internal variables. We don't use this data, so this execution could be safely removed.

[tomyrd]

Thank you for the explanation! I fixed this test and the serial number one.

[Fumuran]

LGTM, thank you!

I left just one comment inline.

[Fumuran]

I think we can avoid importing the Word here by calling the .as_elements() on the RpoDigest returned from the .hash():

let script_hash = tx_context.input_notes().get_note(0).note().script().hash();
assert_eq!(process.stack.get_word(0), script_hash.as_elements());

[Fumuran]

I think we should note this change as breaking, since it changes the offsets of the kernel procedures.

[bobbinth]

Looks good! Thank you!