Another attempt at string encoding for JS inside a PDF.

Fixes https://gitlab.com/kicad/code/kicad/issues/12782

common/string_utils.cpp

@@ -196,7 +196,14 @@ wxString EscapeString( const wxString& aSource, ESCAPE_CONTEXT aContext )
         }
         else if( aContext == CTX_JS_STR )
         {
-            if( c == '\'' )
+            if( c >= 0x7F )
+            {
+                unsigned int code = c;
+                char buffer[16];
+                sprintf( buffer, "\\\\u%4.4X", code );
+                converted += buffer;
+            }
+            else if( c == '\'' )
                 converted += wxT( "{quote}" );
             else if( c == '\\' )
                 converted += wxT( "{backslash}" );