Fix #3025: Annotate nested types

[ltrzesniewski]

Fixes #3025

Problem

• The outer class of a nested class is not clickable #3025

Solution

• Any comments on the approach taken, its consistency with surrounding code, etc.

Normally, AddTypeAnnotation is called right after ConvertTypeHelper in the ConvertType method:

ILSpy/ICSharpCode.Decompiler/CSharp/Syntax/TypeSystemAstBuilder.cs

Lines 244 to 245 in bf0d74d

	AstType astType = ConvertTypeHelper(type);
	AddTypeAnnotation(astType, type);

But in the case of nested types, ConvertTypeHelper calls itself recursively for declaring types, and therefore AddTypeAnnotation was never called for these nodes.

• Which part of this PR is most in need of attention/improvement?

This is a very simple change.

• At least one test covering the code changed

I couldn't find any existing unit tests which check for type annotations (ResolveResult), so I wasn't sure where to put this. If you'd like me to add a unit test, please tell me in which way you'd like for type annotations to be tested.

[siegfriedpammer]

Thank you for your contribution!