Rust: Add query sink counts query for getting a breakdown.

rust/ql/src/queries/summary/QuerySinkCounts.ql

@@ -0,0 +1,17 @@
+/**
+ * @name Query Sink Counts
+ * @description Lists the number of query sinks of each type found in the database. Query sinks are
+ *              flow sinks that are used as possible locations for query results. Cryptographic
+ *              operations are excluded.
+ * @kind metric
+ * @id rust/summary/query-sink-counts
+ * @tags summary
+ */
+
+import rust
+import codeql.rust.dataflow.DataFlow
+import Stats
+
+from string kind, int num
+where num = strictcount(DataFlow::Node n | getAQuerySinkKind(n) = kind)
+select kind, num