Native keyboard behavior update for multiline input (#4234)

Use sentence capitalization for non-obscuretext fields of TextInputType.text
and TextInputType.multiline on iOS and Android.

shell/platform/android/io/flutter/plugin/editing/TextInputPlugin.java

@@ -98,8 +98,11 @@ public class TextInputPlugin implements MethodCallHandler {
             // Note: both required. Some devices ignore TYPE_TEXT_FLAG_NO_SUGGESTIONS.
             textType |= InputType.TYPE_TEXT_FLAG_NO_SUGGESTIONS;
             textType |= InputType.TYPE_TEXT_VARIATION_PASSWORD;
-        } else if (autocorrect) {
+        } else {
+          if (autocorrect)
             textType |= InputType.TYPE_TEXT_FLAG_AUTO_CORRECT;
+          if (inputType.equals("TextInputType.text") || inputType.equals("TextInputType.multiline"))
+            textType |= InputType.TYPE_TEXT_FLAG_CAP_SENTENCES;
         }
         return textType;
     }

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

@@ -34,6 +34,8 @@ static UIReturnKeyType ToUIReturnKeyType(NSString* inputType) {
 static UITextAutocapitalizationType ToUITextAutocapitalizationType(NSString* inputType) {
   if ([inputType isEqualToString:@"TextInputType.text"])
     return UITextAutocapitalizationTypeSentences;
+  if ([inputType isEqualToString:@"TextInputType.multiline"])
+    return UITextAutocapitalizationTypeSentences;
   return UITextAutocapitalizationTypeNone;
 }