[mcs] Fix recursive resolving of crefs (#18511)

The following crefs should all work and resolve to the same member:

&lt;see cref="MyEnum.One"/>
&lt;see cref="Program.MyEnum.One"/>
&lt;see cref="XmlComments.Program.MyEnum.One"/>
&lt;see cref="F:XmlComments.Program.MyEnum.One"/>

Previously only the first and last notation worked.