ILLink analyzer doesn't warn for invalid annotations in top-level methods

[sbomer]

DynamicallyAccessedMembers annotations are not supported for arbitrary types. The ILLink analyzer normally produces IL2098 warnings when the annotations are applied to unsupported types, but this isn't working for top-level methods:

using System.Diagnostics.CodeAnalysis;

RequireAll(GetFoo());

// This should warn
static void RequireAll([DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.All)] Foo f) {}

static Foo GetFoo() => new Foo();

class Foo {}

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[sbomer]

This is blocked on https://github.com/dotnet/roslyn/issues/14061. I can't find a way to register a symbol action in the analyzer that gets called for top-level methods. I tried adding a RegisterSymbolAction for SymbolKind.Parameter, but that faces the same problem as mentioned in https://github.com/dotnet/roslyn/issues/14061#issuecomment-249438327.