feat!: Handle generic fields in StructDefinition::fields and move old functionality to StructDefinition::fields_as_written

[jfecher]

Description

Problem*

Resolves an issue from a private slack request. Needed for implementing derive_serialize recursively so that struct field types have their generics substituted correctly.

Summary*

Adds a generic_args argument to StructDefinition::fields to instantiate the field types with. This means this PR is breaking since this method used to require only self.

Since the old functionality of not instantiating can still be useful, I have moved it to a new function fields_as_written but wanted to emphasize that if users did need field types, and they don't know what the difference is, that they should prefer to use fields.

Additional Context

Documentation*

Check one:

• No documentation needed.
• Documentation included in this PR.
• [For Experimental Features] Documentation to be submitted in a separate PR.

PR Checklist*

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

[github-actions]

Compilation Memory Report

Program	Peak Memory	%
keccak256	77.73M	0%
workspace	123.80M	0%
regression_4709	424.10M	0%
ram_blowup_regression	1.58G	0%
rollup-root	204.23M	-46%
rollup-merge	204.23M	-11%
rollup-block-root-single-tx	204.23M	100%
rollup-block-root-empty	204.23M	-9%
rollup-block-root	204.23M	100%
rollup-block-merge	204.23M	-46%
rollup-base-public	204.23M	100%
rollup-base-private	204.23M	-78%
private-kernel-tail	168.37M	-19%
private-kernel-reset	168.39M	-75%
private-kernel-inner	168.36M	-43%

[github-actions]

Execution Memory Report

Program	Peak Memory	%
keccak256	74.69M	0%
workspace	123.95M	0%
regression_4709	316.01M	0%
ram_blowup_regression	512.61M	0%
rollup-root	204.23M	-12%
rollup-merge	204.23M	-1%
rollup-block-root	204.23M	100%
rollup-block-merge	204.23M	-12%
rollup-base-public	204.23M	-58%
rollup-base-private	204.23M	-38%
private-kernel-tail	168.36M	-7%
private-kernel-reset	168.39M	-32%
private-kernel-inner	168.36M	-20%

[github-actions]

🚀 Deployed on https://6786d32777c5174a76a4468e--noir-docs.netlify.app

[michaeljklein]

LGTM, with small note r.e. using fields on fields_as_written

[github-actions]

FYI @noir-lang/developerrelations on Noir doc changes.

[TomAFrench]

In future please coordinate with me if merging breaking changes which blow up all of our benchmarks. Having this dropped on me when noir syncs are blocked is not fun.

[asterite]

Another thing that might have been good to do, given that this is a breaking change, is to also return the visibility of each field (we also have an issue to be able to set those visibilities when setting those fields)

[jfecher]

@TomAFrench sorry about that, I mistakenly assumed the sync itself would be quick and it'd just break aztec-noir downstream which could be fixed fairly quickly. I'll definitely coordinate more in the future