Revert "[web] Move text editing nodes outside of shadowDOM"

[zanderso]

Reverts #39688

Looks like this is causing the roll to the framework to fail. See https://ci.chromium.org/ui/p/flutter/builders/try/Linux%20web_long_running_tests_4_5/34083/overview

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  JavaScriptException (500): javascript error: Cannot read properties of null (reading 'querySelector')
    (Session info: headless chrome=96.0.4664.0)

  package:webdriver/src/handler/w3c/utils.dart 57:9       parseW3cResponse
  package:webdriver/src/handler/w3c/core.dart 59:19       W3cCoreHandler.parseExecuteResponse
  package:webdriver/src/async/web_driver.dart 260:37      WebDriver.execute.<fn>
  package:webdriver/src/common/request_client.dart 96:32  AsyncRequestClient.send
  ===== asynchronous gap ===========================
  test_driver/smoke_web_engine_test.dart 41:40            main.<fn>.<fn>
  ===== asynchronous gap ===========================
  package:test_api/src/backend/declarer.dart 215:9        Declarer.test.<fn>.<fn>
  ===== asynchronous gap ===========================
  package:test_api/src/backend/declarer.dart 213:7        Declarer.test.<fn>
  ===== asynchronous gap ===========================
  package:test_api/src/backend/invoker.dart 258:9         Invoker._waitForOutstandingCallbacks.<fn>


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