JS: Add UnresolvableImport metric

javascript/ql/src/meta/analysis-quality/UnresolvableImports.ql

@@ -0,0 +1,18 @@
+/**
+ * @name Unresolvable imports
+ * @description The number of imports that could not be resolved to a module.
+ * @kind metric
+ * @metricType project
+ * @metricAggregate sum
+ * @tags meta
+ * @id js/meta/unresolvable-imports
+ */
+
+import javascript
+import CallGraphQuality
+
+Import unresolvableImport() {
+    not exists(result.getImportedModule())
+}
+
+select projectRoot(), count(unresolvableImport())