Feature request: add markup to specify supressed/unsuppressed diagnostics

[DoctorKrolic]

Right now in order to test diagnostic suppressor it is required to use code instead of more visual markup. It might be a good thing to add a pair of markup rules to express this directly there instead of having to dive into code. Therefore I suggest the following:

• if a named span ends with ? treat it as suppressed diagnostic name
• if a named span ends with ! verify that this diagnostic is not suppressed

Consider the following example:

[Fact]
public async Task Test1()
{
    var source = """
        class C
        {
            public string {|#0:Prop|} { get; set; }
            public string {|#1:OtherProp|} { get; set; }
        }
        """;

    await new MyAnalyzerVerifier<MySuppressor>.Test
    {
        TestCode = source,
        ExpectedDiagnostics =
        {
            DiagnosticResult.CompilerWarning("CS8618").WithLocation(0).WithLocation(0).WithIsSuppressed(true)
            DiagnosticResult.CompilerWarning("CS8618").WithLocation(1).WithLocation(1).WithIsSuppressed(false)
        },
        CompilerDiagnostics = CompilerDiagnostics.Warnings
    }.RunAsync();
}

Using proposed rules this test can be simplified to:

[Fact]
public async Task Test1()
{
    var source = """
        class C
        {
            public string {|CS8618?:Prop|} { get; set; }
            public string {|CS8618!:OtherProp|} { get; set; }
        }
        """;

    await new MyAnalyzerVerifier<MySuppressor>.Test
    {
        TestCode = source,
        CompilerDiagnostics = CompilerDiagnostics.Warnings
    }.RunAsync();
}

Not a big deal, just a little quality of life thing.