Add formatting analyzer test for param nullchecking

[RikkiGibson]

Closes #58798.

Adding a test to demonstrate that the formatting analyzer itself isn't at fault here. Just the fact that we are using an old version of it in Roslyn.

[Youssef1313]

Consider adding a test where the !! isn't properly formatted:

class MyClass
{
    void MyMethod(string s !!) // <-- Extra space should be reported and fixed
    {
    }
}

[RikkiGibson]

We have such a test for the formatter itself. It wouldn't hurt to have it for the formatting analyzer too.

roslyn/src/Workspaces/CSharpTest/Formatting/FormattingTests.cs

Lines 5779 to 5799 in 259a9e2

	[Fact]
	[Trait(Traits.Feature, Traits.Features.Formatting)]
	public async Task SpacingInNullCheckedParameter()
	{
	var code =
	@"class C
	{
	static object F(string s !!)
	{
	}
	}";
	var expectedCode =
	@"class C
	{
	static object F(string s!!)
	{
	}
	}";
	await AssertFormatAsync(expectedCode, code);
	}

I did find that we don't do the right thing in the following scenario:

static void M1(string x
    !!)
{
}

I expected !! to always be moved to be right up against the parameter name. It seems like the leading trivia owned by !! should be moved to the next token, for consistency with the following (which doesn't prompt any formatting errors)

static void M1(string x
    )
{
}

All that said, I'd prefer to back-burner this work and possibly make it "help wanted". The important thing I wanted to confirm with this PR is that "correctly formatted" code using the feature doesn't produce formatting warnings.

[CyrusNajmabadi]

I expected !! to always be moved to be right up against the parameter name.

You'll likely need to force-space to 0, and set that without the flag that says only do that when on the same lien.

[RikkiGibson]

Thanks for the review @davidwengier!