Merge pull request #2204 from alexet/cache-to-string

Cache the computation of core toString predicates for cpp c# and java.

Author: jbj

cpp/ql/src/semmle/code/cpp/Element.qll

@@ -47,6 +47,7 @@ pragma[inline]
  */
 class ElementBase extends @element {
   /** Gets a textual representation of this element. */
+  cached
   string toString() { none() }
 
   /**

csharp/ql/src/semmle/code/dotnet/Element.qll

@@ -10,6 +10,7 @@ import semmle.code.csharp.Location
  */
 class Element extends @dotnet_element {
   /** Gets a textual representation of this element. */
+  cached
   string toString() { none() }
 
   /** Gets the location of this element. */