All languages: Add getPrimaryQlClasses()

This is a non-overridable predicate that concatenates all the
getAPrimaryQlClass() results into a comma-separated string.

java/ql/lib/semmle/code/Location.qll

@@ -100,6 +100,11 @@ class Top extends @top {
   cached
   string toString() { hasName(this, result) }
 
+  /**
+   * Gets a comma-separated list of the names of the primary CodeQL classes to which this element belongs.
+   */
+  final string getPrimaryQlClasses() { result = concat(getAPrimaryQlClass(), ",") }
+
   /**
    * Gets the name of a primary CodeQL class to which this element belongs.
    *

java/ql/lib/semmle/code/java/PrintAst.qll

@@ -89,7 +89,7 @@ private predicate duplicateMetadata(Field f) {
  * Retrieves the canonical QL class(es) for entity `el`
  */
 private string getQlClass(Top el) {
-  result = "[" + concat(el.getAPrimaryQlClass(), ",") + "] "
+  result = "[" + el.getPrimaryQlClasses() + "] "
   // Alternative implementation -- do not delete. It is useful for QL class discovery.
   // result = "[" + concat(el.getAQlClass(), ",") + "] "
 }