BEGIN_ILLINK_FEATURE_SWITCH mechanism for `corelib.h` does not work with nested classes

[AaronRobinsonMSFT]

The following doesn't properly work when placed in the generated XML file:

DEFINE_CLASS(UTF8STRINGMARSHALLER_IN, Marshalling, Utf8StringMarshaller+ManagedToUnmanagedIn)

Following the Cecil syntax also fails:

DEFINE_CLASS(UTF8STRINGMARSHALLER_IN, Marshalling, Utf8StringMarshaller/ManagedToUnmanagedIn)

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Issue Details

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The following doesn't properly work when placed in the generated XML file:

DEFINE_CLASS(UTF8STRINGMARSHALLER_IN, Marshalling, Utf8StringMarshaller+ManagedToUnmanagedIn)

Following the Cecil syntax also fails:

DEFINE_CLASS(UTF8STRINGMARSHALLER_IN, Marshalling, Utf8StringMarshaller/ManagedToUnmanagedIn)

Author:	AaronRobinsonMSFT
Assignees:	-
Labels:	area-Interop-coreclr, linkable-framework
Milestone:	7.0.0