[web] new text editing method.

[nturgut]

web engine should not give an error for the new text editing method. This PR is good to have before PR: flutter/flutter#52126

Since the web engine starts returning Bad State Error for every autofill field, filling the log with red warnings:

Error: Bad state: Unsupported method call on the flutter/textinput channel: TextInput.requestAutofill
    at Object.throw_ [as throw] (http://localhost:8080/dart_sdk.js:4040:11)
    at _engine.TextEditingChannel.new.handleTextInput (http://localhost:8080/dart_sdk.js:160283:21)
    at _engine.EngineWindow.new.[_sendPlatformMessage] (http://localhost:8080/dart_sdk.js:162238:39)
    at _engine.EngineWindow.new.sendPlatformMessage (http://localhost:8080/dart_sdk.js:162158:33)
    at _DefaultBinaryMessenger.[_sendPlatformMessage] (http://localhost:8080/packages/flutter/src/services/platform_channel.dart.lib.js:1357:17)
    at _DefaultBinaryMessenger.send (http://localhost:8080/packages/flutter/src/services/platform_channel.dart.lib.js:1393:40)
    at OptionalMethodChannel._invokeMethod (http://localhost:8080/packages/flutter/src/services/platform_channel.dart.lib.js:367:50)
    at _invokeMethod.next (<anonymous>)

[LongCatIsLooong]

LGTM. Thank you!

[nturgut]

Merging the PR:
(1) Changes are unrelated to Fushia build.
(2) The Mac Web Engine had an infra issue and I restarted the task. The updated results are not synced to github but they were successful. Successful MacWebEngine run for this PR: https://ci.chromium.org/p/flutter/builders/try/Mac%20Web%20Engine/2156