Fix finding xml help files in Visual Studio.

We should pass the location of the metadata file to the
IVsXmlMemberIndexService than passing the location of the xml help file.
IVsXmlMemberIndexService locates the help file by looking at
appropriate locations such as localized directories or the root
directory where the metadata file is present. This change removes
calling our utility to locate the help file in the VS provider (the helper
is probably meant for internal test applications and such). This fixes a
bug where we were unable to find xml help files for WinMds in the fall
back case where people place help file next to winmds for cultures that
help file wasn't translated for. In such cases, the user should get the
english documentation.

src/VisualStudio/Core/Def/Implementation/ProjectSystem/MetadataReferences/VisualStudioMetadataReference.Snapshot.cs

@@ -82,15 +82,7 @@ private bool SaveMetadataReadingException(Exception e)
 
             protected override DocumentationProvider CreateDocumentationProvider()
             {
-                string xmlDocumentPath;
-                if (ReferencePathUtilities.TryFindXmlDocumentationFile(FilePath, out xmlDocumentPath))
-                {
-                    return new VisualStudioDocumentationProvider(xmlDocumentPath, _provider.XmlMemberIndexService);
-                }
-                else
-                {
-                    return DocumentationProvider.Default;
-                }
+                return new VisualStudioDocumentationProvider(this.FilePath, _provider.XmlMemberIndexService);
             }
 
             protected override PortableExecutableReference WithPropertiesImpl(MetadataReferenceProperties properties)