chore(ssa gen): ssa gen truncate instruction

[joss-aztec]

Description

Problem*

Summary*

This PR sets out to code gen truncate instructions

Example

fn main(x : u2) -> pub u2 {
    1 - x
}

compiles to

current witness index : 4
public parameters indices : []
return value indices : [2]
BLACKBOX::RANGE [(_1, num_bits: 2)] [ ]
DIR::QUOTIENT (out : _%EXPR [ (-1, _1) 5 ]%,  (_3, %EXPR [ 4 ]%), _2)
BLACKBOX::RANGE [(_2, num_bits: 2)] [ ]
BLACKBOX::RANGE [(_3, num_bits: 1)] [ ]
EXPR [ (1, _1) (1, _2) (4, _3) -5 ]

Documentation

• This PR requires documentation updates when merged.

  • I will submit a noir-lang/docs PR.
  • I will request for and support Dev Rel's help in documenting this PR.

Additional Context

PR Checklist*

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.

[jfecher]

(In the process of reviewing still, apologies for the delay)

[joss-aztec]

Had to address #1624 in order to get brillig_integer_binary_operations test working.

spoke internally and we will revisit the topic of whether truncate can be made simpler