visiblePassword uses ASCII keyboard on iOS (#50293)

Fixes flutter/flutter#129113

The documentation states that the `visiblePassword` input type
> Requests a keyboard with ready access to both letters and numbers.

`UIKeyboardTypeASCIICapable` seems to be the closest match.

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

Author: LongCatIsLooong

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

@@ -137,6 +137,9 @@ static UIKeyboardType ToUIKeyboardType(NSDictionary* type) {
   if ([inputType isEqualToString:@"TextInputType.url"]) {
     return UIKeyboardTypeURL;
   }
+  if ([inputType isEqualToString:@"TextInputType.visiblePassword"]) {
+    return UIKeyboardTypeASCIICapable;
+  }
   return UIKeyboardTypeDefault;
 }
 

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

@@ -307,6 +307,20 @@ - (void)testKeyboardType {
   XCTAssertEqual(inputView.keyboardType, UIKeyboardTypeURL);
 }
 
+- (void)testVisiblePasswordUseAlphanumeric {
+  NSDictionary* config = self.mutableTemplateCopy;
+  [config setValue:@{@"name" : @"TextInputType.visiblePassword"} forKey:@"inputType"];
+  [self setClientId:123 configuration:config];
+
+  // Find all the FlutterTextInputViews we created.
+  NSArray<FlutterTextInputView*>* inputFields = self.installedInputViews;
+
+  FlutterTextInputView* inputView = inputFields[0];
+
+  // Verify keyboardType is set to the value specified in config.
+  XCTAssertEqual(inputView.keyboardType, UIKeyboardTypeASCIICapable);
+}
+
 - (void)testSettingKeyboardTypeNoneDisablesSystemKeyboard {
   NSDictionary* config = self.mutableTemplateCopy;
   [config setValue:@{@"name" : @"TextInputType.none"} forKey:@"inputType"];