C++: Add a predicate for getting the 0'th child of a 'ConditionDeclExpr' without casting it to a 'VariableAccess' and use it in IR generation.

cpp/ql/lib/semmle/code/cpp/ir/implementation/raw/internal/TranslatedExpr.qll

@@ -3173,7 +3173,7 @@ class TranslatedConditionDeclExpr extends TranslatedNonConstantExpr {
   private TranslatedConditionDecl getDecl() { result = getTranslatedConditionDecl(expr) }
 
   private TranslatedExpr getConditionExpr() {
-    result = getTranslatedExpr(expr.getVariableAccess().getFullyConverted())
+    result = getTranslatedExpr(expr.getExpr().getFullyConverted())
   }
 }