Use the Noto fonts from the C++ build of the printer demo

This adds API to register a font by path from C++

api/sixtyfps-cpp/include/sixtyfps_string.h

@@ -85,6 +85,9 @@ struct SharedString
     const char *begin() const { return data(); }
     const char *end() const { return &*std::string_view(*this).end(); }
 
+    /// \return true if the string contains no characters; false otherwise.
+    bool empty() const { return std::string_view(*this).empty(); }
+
     /// Creates a new SharedString from the given number \a n. The string representation of the
     /// number uses a minimal formatting scheme: If \a n has no fractional part, the number will be
     /// formatted as an integer.