Add Look Up to iOS selection controls (flutter#43308)

In native iOS, when Look Up is initiated on highlighted text, a view DDParsecCollectionViewController is presented with definitions of the the selected text if available, as well as Siri integrated suggestions. However, since the view controller is gated behind a private API, we will use [UIReferenceLibraryViewController](https://developer.apple.com/documentation/uikit/uireferencelibraryviewcontroller) instead, which is functionally identical and visually very similar.

| Native | UIReferenceLibraryViewController|
| ------------- | ------------- |
| <img src="https://github.com/flutter/engine/assets/36148254/763004f0-970f-4d8a-9a9a-133401ef0c1b" width="360" />| <img src="https://github.com/flutter/engine/assets/36148254/b20fe03f-6c9d-4a4a-98dc-8bcd840406db" width="360" />|

This PR is the engine portion of the changes that will allow this feature change.
This PR addresses flutter/flutter#82907
More details are available in this [design doc](flutter.dev/go/add-missing-features-to-selection-controls)

Author: LouiseHsu

shell/platform/darwin/ios/framework/Source/FlutterPlatformPlugin.mm

@@ -115,6 +115,9 @@ - (void)handleMethodCall:(FlutterMethodCall*)call result:(FlutterResult)result {
     result([self clipboardHasStrings]);
   } else if ([method isEqualToString:@"LiveText.isLiveTextInputAvailable"]) {
     result(@([self isLiveTextInputAvailable]));
+  } else if ([method isEqualToString:@"LookUp.invoke"]) {
+    [self showLookUpViewController:args];
+    result(nil);
   } else {
     result(FlutterMethodNotImplemented);
   }
@@ -307,6 +310,16 @@ - (BOOL)isLiveTextInputAvailable {
   return [[self textField] canPerformAction:@selector(captureTextFromCamera:) withSender:nil];
 }
 
+- (void)showLookUpViewController:(NSString*)term {
+  UIViewController* engineViewController = [_engine.get() viewController];
+  FML_DCHECK(![engineViewController presentingViewController]);
+  UIReferenceLibraryViewController* referenceLibraryViewController =
+      [[[UIReferenceLibraryViewController alloc] initWithTerm:term] autorelease];
+  [engineViewController presentViewController:referenceLibraryViewController
+                                     animated:YES
+                                   completion:nil];
+}
+
 - (UITextField*)textField {
   if (_textField == nil) {
     _textField = [[UITextField alloc] init];

shell/platform/darwin/ios/framework/Source/FlutterPlatformPluginTest.mm

@@ -17,10 +17,48 @@ @interface FlutterPlatformPluginTest : XCTestCase
 
 @interface FlutterPlatformPlugin ()
 - (BOOL)isLiveTextInputAvailable;
+- (void)showLookUpViewController:(NSString*)term;
+@end
+
+@interface UIViewController ()
+- (void)presentViewController:(UIViewController*)viewControllerToPresent
+                     animated:(BOOL)flag
+                   completion:(void (^)(void))completion;
 @end
 
 @implementation FlutterPlatformPluginTest
 
+- (void)testLookUpCallInitiated {
+  FlutterEngine* engine = [[[FlutterEngine alloc] initWithName:@"test" project:nil] autorelease];
+  [engine runWithEntrypoint:nil];
+  std::unique_ptr<fml::WeakPtrFactory<FlutterEngine>> _weakFactory =
+      std::make_unique<fml::WeakPtrFactory<FlutterEngine>>(engine);
+
+  XCTestExpectation* presentExpectation =
+      [self expectationWithDescription:@"Look Up view controller presented"];
+
+  FlutterViewController* engineViewController = [[FlutterViewController alloc] initWithEngine:engine
+                                                                                      nibName:nil
+                                                                                       bundle:nil];
+  FlutterViewController* mockEngineViewController = OCMPartialMock(engineViewController);
+
+  FlutterPlatformPlugin* plugin =
+      [[[FlutterPlatformPlugin alloc] initWithEngine:_weakFactory->GetWeakPtr()] autorelease];
+  FlutterPlatformPlugin* mockPlugin = OCMPartialMock(plugin);
+
+  FlutterMethodCall* methodCall = [FlutterMethodCall methodCallWithMethodName:@"LookUp.invoke"
+                                                                    arguments:@"Test"];
+  FlutterResult result = ^(id result) {
+    OCMVerify([mockEngineViewController
+        presentViewController:[OCMArg isKindOfClass:[UIReferenceLibraryViewController class]]
+                     animated:YES
+                   completion:nil]);
+    [presentExpectation fulfill];
+  };
+  [mockPlugin handleMethodCall:methodCall result:result];
+  [self waitForExpectationsWithTimeout:2 handler:nil];
+}
+
 - (void)testClipboardHasCorrectStrings {
   [UIPasteboard generalPasteboard].string = nil;
   FlutterEngine* engine = [[[FlutterEngine alloc] initWithName:@"test" project:nil] autorelease];