CS4033 creates invalid code on partial methods

[MisinformedDNA]

Version Used: VS 2022 17.3.0

Steps to Reproduce:

1. Implement a partial method
2. Add an async call
3. Use code fix "Make method async (stay void)"

using System.Threading.Tasks;

public partial class C {
    partial void M();
}

public partial class C {
    partial void M() {
        await Task.Delay(1);
    }
}

Expected Behavior:

Generates valid code:

    async partial void M() {
        await Task.Delay(1);
    }

Actual Behavior:

Generates invalid code. async needs to come before partial

    partial async void M() {
        await Task.Delay(1);
    }

[Youssef1313]

@CyrusNajmabadi Should we respect editorconfig's modifier order preference as part of the cleanup process that's run on every code action?

roslyn/src/Workspaces/Core/Portable/CodeActions/CodeAction.cs

Lines 329 to 346 in 98139d7

	internal static async Task<Document> CleanupDocumentAsync(
	Document document, CodeCleanupOptions options, CancellationToken cancellationToken)
	{
	document = await ImportAdder.AddImportsFromSymbolAnnotationAsync(
	document, Simplifier.AddImportsAnnotation, options.AddImportOptions, cancellationToken).ConfigureAwait(false);
	document = await Simplifier.ReduceAsync(document, Simplifier.Annotation, options.SimplifierOptions, cancellationToken).ConfigureAwait(false);
	// format any node with explicit formatter annotation
	document = await Formatter.FormatAsync(document, Formatter.Annotation, options.FormattingOptions, cancellationToken).ConfigureAwait(false);
	// format any elastic whitespace
	document = await Formatter.FormatAsync(document, SyntaxAnnotation.ElasticAnnotation, options.FormattingOptions, cancellationToken).ConfigureAwait(false);
	document = await CaseCorrector.CaseCorrectAsync(document, CaseCorrector.Annotation, cancellationToken).ConfigureAwait(false);
	return document;
	}

possibly via a reducer?

roslyn/src/Workspaces/CSharp/Portable/Simplification/CSharpSimplificationService.cs

Lines 27 to 39 in 98139d7

	private static readonly ImmutableArray<AbstractReducer> s_reducers =
	ImmutableArray.Create<AbstractReducer>(
	new CSharpVarReducer(),
	new CSharpNameReducer(),
	new CSharpNullableAnnotationReducer(),
	new CSharpCastReducer(),
	new CSharpExtensionMethodReducer(),
	new CSharpParenthesizedExpressionReducer(),
	new CSharpParenthesizedPatternReducer(),
	new CSharpEscapingReducer(),
	new CSharpMiscellaneousReducer(),
	new CSharpInferredMemberNameReducer(),
	new CSharpDefaultExpressionReducer());

[dibarbet]

This seems to be broken in general as it also does not make the other partial definition return Task. We should also respect order modifiers, but we should also generate non-broken code (which I think we can here).