Define class Identifier and template TaggedIdentifier...

... Identifier holds strings used for internal purposes and not shown to users;
TaggedIdentifier generates subclasses of Identifier for different purposes,
which won't implicitly (that is, inadvertently) interconvert as function
arguments.

src/Internat.cpp

@@ -310,3 +310,25 @@ wxArrayStringEx LocalizedStrings(
       std::mem_fn( &EnumValueSymbol::Translation )
    );
 }
+
+// Find a better place for this?
+#include "audacity/Types.h"
+Identifier::Identifier(
+                       std::initializer_list<Identifier> components, wxChar separator )
+{
+   if( components.size() < 2 )
+   {
+      wxASSERT( false );
+      return;
+   }
+   auto iter = components.begin(), end = components.end();
+   value = (*iter++).value;
+   while (iter != end)
+      value += separator + (*iter++).value;
+}
+
+std::vector< Identifier > Identifier::split( wxChar separator ) const
+{
+   auto strings = ::wxSplit( value, separator );
+   return { strings.begin(), strings.end() };
+}