fix: Various fixes for defunctionalization & brillig gen

[sirasistant]

Description

• Fix register overwrite when returning from functions that return more than two registers (Resolves Calling a function that returns more than two registers corrupts the registers of the caller #1976)
• Extract convert function call to its own method
• Allow lessthan operations for comparisons of fields issued by the compiler (loops) (Resolves Iterating with a literal range in brillig panics the compiler #1977)
• Refactor defunctionalization
  • No longer try to guess runtime of callees (Resolves Defunctionalization should ignore the runtime of the functions being called #1974)
  • Use Signature struct of ssa ir
  • Fix dynamic dispatch collection
  • Fix transformation of functions as values to numeric constants (Resolves Defunctionalization breaks if a function is used both as literal and as a value #1975)

Problem*

Summary*

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.

[ludamad]

Some stuff with defunctionalize seem that they could use a pass to read less like the raw data structure manipulation operations or raw SSA traversal for function values, but I rather merge fast and let you ponder that longer

LGTM

[jfecher]

Also, can we split this up into smaller PRs next time (ideally one per issue)? Many of these changes seem unrelated and this PR solving several issues makes each individual fix more difficult to isolate. It's also easier reviewing several smaller PRs than one larger one, especially if part of the larger PR becomes blocking for the rest of it.