C#: Refactor and narrow number of displayed results of the External library usage query.

Author: michaelnebel

csharp/ql/src/Telemetry/ExternalLibraryUsage.ql

@@ -10,12 +10,28 @@ private import csharp
 private import semmle.code.csharp.dispatch.Dispatch
 private import ExternalApi
 
-from int usages, string info
-where
+private predicate getRelevantUsages(string info, int usages) {
   usages =
     strictcount(DispatchCall c, ExternalApi api |
       c = api.getACall() and
       api.getInfoPrefix() = info and
       not api.isUninteresting()
     )
+}
+
+private int getOrder(string info) {
+  info =
+    rank[result](string i, int usages |
+      exists(ExternalApi api | i = api.getInfoPrefix()) and
+      getRelevantUsages(i, usages)
+    |
+      i order by usages desc, i
+    )
+}
+
+from ExternalApi api, string info, int usages
+where
+  info = api.getInfoPrefix() and
+  getRelevantUsages(info, usages) and
+  getOrder(info) <= resultLimit()
 select info, usages order by usages desc