Define and use function Verbatim...

... in cases of "TranslatableString" that are not really translated.

This makes it easier to scan the code for such unusual constructions of
TranslatableString, distinct from mere mentions of the TranslatableString type.

include/audacity/Types.h

@@ -308,23 +308,20 @@ class TranslatableString : private wxString {
    template< size_t N > struct PluralTemp;
 
 public:
+   // A special string value that will have no screen reader pronunciation
+   static const TranslatableString Inaudible;
+
    // A multi-purpose function, depending on the enum argument; the string
    // argument is unused in some cases
    // If there is no function, defaults are empty context string, no plurals,
    // and no substitutions
    using Formatter = std::function< wxString(const wxString &, Request) >;
 
-   // This special formatter causes msgids to be used verbatim, not looked up
-   // in any catalog, so Translation() and Debug() return the same
-   static const Formatter NullContextFormatter;
-
    TranslatableString() {}
 
    // Supply {} for the second argument to cause lookup of the msgid with
    // empty context string (default context) rather than the null context
-   explicit TranslatableString(
-      wxString str, Formatter formatter = NullContextFormatter
-   )
+   explicit TranslatableString( wxString str, Formatter formatter )
       : mFormatter{ std::move(formatter) }
    {
       this->wxString::swap( str );
@@ -472,6 +469,18 @@ public:
    { return TranslatableString{ *this }.Strip( options ); }
 
 private:
+   static const Formatter NullContextFormatter;
+
+   // Construct a TranslatableString that does no translation but passes
+   // str verbatim
+   explicit TranslatableString( wxString str )
+      : mFormatter{ NullContextFormatter }
+   {
+      this->wxString::swap( str );
+   }
+
+   friend TranslatableString Verbatim( wxString str );
+
    enum class Request {
       Context,     // return a disambiguating context string
       Format,      // Given the msgid, format the string for end users
@@ -544,9 +553,6 @@ inline TranslatableString operator +(
 
 using TranslatableStrings = std::vector<TranslatableString>;
 
-// A special string value that will have no screen reader pronunciation
-extern const TranslatableString InaudibleString;
-
 // For using std::unordered_map on TranslatableString
 // Note:  hashing on msgids only, which is not all of the information
 namespace std
@@ -561,6 +567,12 @@ namespace std
    };
 }
 
+// Require calls to the one-argument constructor to go through this
+// distinct global function name.  This makes it easier to locate and
+// review the uses of this function, separately from the uses of the type.
+inline TranslatableString Verbatim( wxString str )
+{ return TranslatableString( std::move( str ) ); }
+
 // ----------------------------------------------------------------------------
 // A native 64-bit integer...used when referring to any number of samples
 // ----------------------------------------------------------------------------