[Analyzer] Generate warnings for DebuggerDisplay attributes referencing RUC code

[MichalStrehovsky]

ILLink generates warning for this, the analyzer should too.

We should probably share the logic that is used to parse the DebuggerDisplay string. ILLink also has some special logic to not generate a warning if it doesn't understand the string (the string could be still valid, but ILLink has a simple algorithm to parse it).

using System.Diagnostics;
using System.Diagnostics.CodeAnalysis;

[DebuggerDisplay("{Blah}")]
class Program
{
    public string Blah
    {
        [RequiresUnreferencedCode("Nope")]
        get => "Hello";
    }

    static void Main() => Console.WriteLine("Hi");
}

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[Sergio0694]

Are all of these warnings automatically suppressed when PublishAot=true and DebuggerSupport=false? Should they? 🤔

[MichalStrehovsky]

NativeAOT doesn't have a debugger that would benefit from this so it doesn't look at DebuggerDisplay at all.

ILLinker will drop these if DebuggerSupport=false, yes.

(The Roslyn analyzer should however warn because it has no idea whether/how it will be used.)

[AArnott]

(The Roslyn analyzer should however warn because it has no idea whether/how it will be used.)

If the roslyn analyzer can read DebuggerSupport, then it'll know whether DebuggerDisplayAttribute needs to be parsed. If we don't know of any other use of the attribute, that seems sufficient.