JavaScript: Consolidate ModuleImportNode tests.

Note that `CustomImport.ql` is still separate since it customises the standard library and would hence influennce other tests.

javascript/ql/test/library-tests/ModuleImportNodes/ModuleImportNode_getAMemberInvocation.qll

@@ -0,0 +1,7 @@
+import javascript
+
+query predicate test_ModuleImportNode_getAMemberInvocation(
+  DataFlow::ModuleImportNode m, DataFlow::InvokeNode res
+) {
+  res = m.getAMemberInvocation(_)
+}