GetDisplayName() and FullName use different notation for nested classes

[jtschuster]

The GetDisplayName extension method uses "." as path delimiters for nested classes, but the FullName member uses "/".

MessageContainer.cs appends either the GetDisplayName string or FullPath to the warnings, and strings passed in usually use GetDisplayName.

if (Origin?.Provider is MethodDefinition method)
	sb.Append (method.GetDisplayName ());
else if (Origin?.Provider is IMemberDefinition member)
	sb.Append (member.FullName);
else if (Origin?.Provider is AssemblyDefinition assembly)
	sb.Append (assembly.Name.Name);
else
	throw new NotSupportedException ();

This leads to different looking paths in the same warning:

Trim analysis warning IL2109: Mono.Linker.Tests.Cases.RequiresCapability.RequiresCapability/RequiresOnClass/DerivedWithoutRequires: Type 'Mono.Linker.Tests.Cases.RequiresCapability.RequiresCapability.RequiresOnClass.DerivedWithoutRequires' derives from 'Mono.Linker.Tests.Cases.RequiresCapability.RequiresCapability.RequiresOnClass.ClassWithRequires' which has 'RequiresUnreferencedCodeAttribute'.  Message for --ClassWithRequires--.

[vitek-karas]

Everything written to the diagnostic message should use GetDisplayName. This is a bit complicated but basically there are 4 competing formats how to represent any member:

• Cecil's format - that's what FullName returns - this is implemented by Cecil itself. We also use this format in the linker XML's since that's what linker has been doing since forever - and Cecil supports parsing such format.
• Reflection format - this is what runtime returns from properties like Type.FullName. Michal is actually advertising for use to use this format in the linker. There's definitely merit to that - the reflection format is universal (not language dependent) and easy to lookup when debugging. The linker should not be too language specific - currently it's very pro-C# and cons-Everything else.
• C#/Roslyn format - this is what Roslyn/C# uses - this more or less matches C# syntax (with some caveats). Currently this is what the GetDisplayName tries to produce - the thinking was to produce the same text as the Roslyn analyzers.
• Documentation format - we have a copy of the parser (and writer) for this from Roslyn here - updated to work on top of Cecil. This is the format uses in for example DynamicDependency attribute (I think).

Currently diagnostics is trying to use the C#/Roslyn format, so all messages should use GetDisplayName instead of ToString or FullName (which would produce Cecil's representation).

[jtschuster]

Closed by PR #2449