Refactoring: checkType && checkImplicitCast returned to DataFlowUtils, PROCESSED unboxing returned, StringTemplateVisitor made local

compiler/testData/diagnostics/tests/smartCasts/loops/ifBreakAssignInsideDoWhile.kt

@@ -3,7 +3,9 @@ fun bar(): Boolean { return true }
 public fun foo(x: String?): Int {
     var y: Any
     do {
-        y = ""
+        // This and hashCode() below are needed just to prevent 
+        // UNINITIALIZED_VARIABLE, UNUSED_VALUE, ...
+        y = "" 
         y = if (x == null) break else <!DEBUG_INFO_SMARTCAST!>x<!>
     } while (bar())
     y.hashCode()