chore(ssa refactor): Add pass to simplify the control flow graph

[jfecher]

Related issue(s)

Resolves #

Description

Summary of changes

Adds a simple pass to simplify a function's CFG by inlining a block into its predecessor if that block only has 1 predecessor and that predecessor's only successor is that block. Example before this pass:

fn main {
  b0():
    jmp b1(Field 7)
  b1(v0: Field):
    jmp b2(v0)
  b2(v1: Field):
    return v1
}

And after the pass:

fn main {
  b0():
    return Field 7
}

In the future this pass is expected to perform some other quick tasks like unreachable block elimination. I favored getting this PR out earlier and smaller so that each extra feature could be a separate, easier to review PR.
This pass' name and functionality was inspired by llvm's pass of the same name: https://llvm.org/docs/Passes.html#simplifycfg-simplify-the-cfg.

Dependency additions / changes

Test additions / changes

Checklist

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt with default settings.
• I have linked this PR to the issue(s) that it resolves.
• I have reviewed the changes on GitHub, line by line.
• I have ensured all changes are covered in the description.

Documentation needs

• This PR requires documentation updates when merged.

Additional context

[joss-aztec]

The code seems to imply that there should be some sort of try_inline_into_predecessor failure handling, but currently ignores it. Were you maybe intending to add some info logging?