[Ide] Simpler culture specific resource file template fix

The original fix to allow culture specific resource files (e.g.
Resources.de.resx) to be created by the New File dialog broke how
the ${Name} property was generated in new files. This could cause
invalid C# code to be generated for a new C# file. A simpler fix
is to not use "${Name}.resx" for the name of the file template but
specify a default file extension. This allows culture specific
.resx files to be created and also matches the behaviour of the
C# file template, which already supports creating new files with
a dotted name (e.g. Resources.Designer.cs)

Fixes VSTS #733182 - Invalid C# file created with new Library project
Fixes VSTS #579048 - Unable to  create a culture specific resx files
through the 'New File ..' menu in the Solutions Explorer right click.

main/src/core/MonoDevelop.Ide/templates/EmptyResourceFile.xft.xml

@@ -12,7 +12,7 @@
 
 	<TemplateFiles>
 		<ProjectResource>
-				<File name="${Name}.resx" CustomTool="ResXFileCodeGenerator">
+				<File DefaultExtension=".resx" CustomTool="ResXFileCodeGenerator">
 <![CDATA[<?xml version="1.0" encoding="utf-8"?>
 <root>
 	<resheader name="resmimetype">