Implement interface produces incorrect code for manual use of DefaultParameterValue and Optional

[sharwell]

Two Implement Interface tests reveal broken code when DefaultParameterValue and Optional are used:

roslyn/src/EditorFeatures/CSharpTest/ImplementInterface/ImplementInterfaceTests.cs

Lines 5111 to 5171 in 51c367a

	[WorkItem(545793, "http://vstfdevdiv:8080/DevDiv2/DevDiv/_workitems/edit/545793")]
	[Fact, Trait(Traits.Feature, Traits.Features.CodeActionsImplementInterface)]
	public async Task TestMultiDimArray()
	{
	await TestWithAllCodeStyleOptionsOffAsync(
	@"using System.Runtime.InteropServices;
	interface I
	{
	void Goo([Optional][DefaultParameterValue(1)] int x, int[,] y);
	}
	class C : {|CS0535:I|}
	{
	}",
	@"using System.Runtime.InteropServices;
	interface I
	{
	void Goo([Optional][DefaultParameterValue(1)] int x, int[,] y);
	}
	class C : I
	{
	public void Goo([{|CS1745:DefaultParameterValue|}(1), {|CS1745:Optional|}] int x = {|CS8017:1|}, int[,] y = null)
	{
	throw new System.NotImplementedException();
	}
	}");
	}
	[WorkItem(545794, "http://vstfdevdiv:8080/DevDiv2/DevDiv/_workitems/edit/545794")]
	[Fact, Trait(Traits.Feature, Traits.Features.CodeActionsImplementInterface)]
	public async Task TestParametersAfterOptionalParameter()
	{
	await TestWithAllCodeStyleOptionsOffAsync(
	@"using System.Runtime.InteropServices;
	interface I
	{
	void Goo([Optional, DefaultParameterValue(1)] int x, int[] y, int[] z);
	}
	class C : {|CS0535:I|}
	{
	}",
	@"using System.Runtime.InteropServices;
	interface I
	{
	void Goo([Optional, DefaultParameterValue(1)] int x, int[] y, int[] z);
	}
	class C : I
	{
	public void Goo([{|CS1745:DefaultParameterValue|}(1), {|CS1745:Optional|}] int x = {|CS8017:1|}, int[] y = null, int[] z = null)
	{
	throw new System.NotImplementedException();
	}
	}");
	}

🐛 this code generation is not correct. I'm guess the result we want is:

    public void Goo(int x = 1, int[,] y = null)

Originally posted by @sharwell in #54310 (comment)

[CyrusNajmabadi]

Closing out as not a priority for us. Manual application of these attributes is a not an important scenario.