C#: Port the java FrameworkCoverage query.

csharp/ql/src/Metrics/Summaries/FrameworkCoverage.ql

@@ -0,0 +1,18 @@
+/**
+ * @id csharp/summary/framework-coverage
+ * @name Metrics of framework coverage
+ * @description Expose metrics for the number of API endpoints covered by CSV models.
+ * @kind metric
+ * @tags summary
+ */
+
+import csharp
+import semmle.code.csharp.dataflow.ExternalFlow
+
+from string namespaceAndType, int rows
+where
+  exists(string namespace, string type |
+    namespaceAndType = namespace + ";" + type and
+    rows = strictsum(int n, string kind | modelCoverage(namespace, _, kind, type, n) | n)
+  )
+select namespaceAndType, rows