Add isExcluded/3 that includes the reason for exclusion

This is used for debugging and testing purposes and cannot be used in
our standard queries due to the required negation and the possible
infinite possible values for reason.

Author: rvermeulen

Diff for: cpp/common/src/codingstandards/cpp/Exclusions.qll

@@ -25,12 +25,15 @@ predicate isExcluded(Element e) {
 }
 
 bindingset[e, query]
-predicate isExcluded(Element e, Query query) {
-  e instanceof ExcludedElement
+predicate isExcluded(Element e, Query query) { isExcluded(e, query, _) }
+
+bindingset[e, query]
+predicate isExcluded(Element e, Query query, string reason) {
+  e instanceof ExcludedElement and reason = "Element is an excluded element."
   or
-  e.getFile() instanceof ExcludedFile
+  e.getFile() instanceof ExcludedFile and reason = "Element is part of an excluded file."
   or
-  not exists(e.getFile())
+  not exists(e.getFile()) and reason = "Element is not part of the source repository."
   or
   // There exists a `DeviationRecord` that applies to this element and query, and the query's effective category permits deviation.
   query.getEffectiveCategory().permitsDeviation() and
@@ -39,7 +42,8 @@ predicate isExcluded(Element e, Query query) {
     exists(string path |
       dr.isDeviated(query, path) and
       e.getFile().getRelativePath().prefix(path.length()) = path
-    )
+    ) and
+    reason = "Query has an associated deviation record for the element's file."
     or
     // The element is on the same line as a suppression comment
     exists(Comment c |
@@ -51,6 +55,8 @@ predicate isExcluded(Element e, Query query) {
         e.getLocation().hasLocationInfo(filepath, _, _, endLine, _) and
         c.getLocation().hasLocationInfo(filepath, endLine, _, _, _)
       )
-    )
+    ) and
+    reason =
+      "Query has an associated deviation record with a code identifier that is applied to the element."
   )
 }