[NFC] Refactor getRenameDecl to use the request evaluator

Move `getRenameDecl` from `PrintAsObjC` into its own request so that
other components can re-use this functionality.

lib/AST/Module.cpp

@@ -1638,6 +1638,32 @@ Fingerprint ModuleDecl::getFingerprint() const {
   return Fingerprint{std::move(hasher)};
 }
 
+bool ModuleDecl::isExternallyConsumed() const {
+  // Modules for executables aren't expected to be consumed by other modules.
+  // This picks up all kinds of entrypoints, including script mode,
+  // @UIApplicationMain and @NSApplicationMain.
+  if (hasEntryPoint()) {
+    return false;
+  }
+
+  // If an implicit Objective-C header was needed to construct this module, it
+  // must be the product of a library target.
+  if (!getImplicitImportInfo().BridgingHeaderPath.empty()) {
+    return false;
+  }
+
+  // App extensions are special beasts because they build without entrypoints
+  // like library targets, but they behave like executable targets because
+  // their associated modules are not suitable for distribution.
+  if (getASTContext().LangOpts.EnableAppExtensionRestrictions) {
+    return false;
+  }
+
+  // FIXME: This is still a lousy approximation of whether the module file will
+  // be externally consumed.
+  return true;
+}
+
 //===----------------------------------------------------------------------===//
 // Cross-Import Overlays
 //===----------------------------------------------------------------------===//