Swift: extract ImportDecl and ModuleDecl

As `ASTMangler` crashes when called on `ModuleDecl`, we simply use
its name.

This might probably not work reliably in a scenario where multiple
modules are compiled with the same name (like `main`), but this is left
for future work. At the moment this cannot create DB inconsistencies.

swift/ql/test/extractor-tests/generated/decl/ModuleDecl/ModuleDecl.ql

@@ -0,0 +1,15 @@
+// generated by codegen/codegen.py
+import codeql.swift.elements
+import TestUtils
+
+from
+  ModuleDecl x, Type getInterfaceType, string getName, string isBuiltinModule, string isSystemModule
+where
+  toBeTested(x) and
+  not x.isUnknown() and
+  getInterfaceType = x.getInterfaceType() and
+  getName = x.getName() and
+  (if x.isBuiltinModule() then isBuiltinModule = "yes" else isBuiltinModule = "no") and
+  if x.isSystemModule() then isSystemModule = "yes" else isSystemModule = "no"
+select x, "getInterfaceType:", getInterfaceType, "getName:", getName, "isBuiltinModule:",
+  isBuiltinModule, "isSystemModule:", isSystemModule