Converting USTR to CSTR in concatenation

The Titan compiler cannot convert universal charstring literals to charstring, if it's inside an unfoldable (i.e. not known at compile-time) concatenation expression.

Example:

var charstring vl_removables := " " & char(0,0,0,27) & "\[[DAK]"; // ok
vl_removables := vl_removables & "|" & "\[[DAK] "; // ok
 
vl_removables := vl_removables & "|" & "\[[DAK] " & char(0,0,0,27); // not ok
 
vl_removables := char(0,0,0,27); // ok
 
vl_removables := char(0,0,0,27) & vl_removables; // not ok

/cc @aknappqwt @mmagyari