Refactoring text editing. Strategy pattern is used to handle different browser/operating system and a11y behavior. (#14131)

* adding the default text editing strategy

* [DRAFT] Refactoring text editing. Strategy pattern is used to handle different browser/operating system and a11y behaviour. Unit tests are missing. Documentation needs updating.

* addressing PR comments

* addressing PR comments. Fixing documentation

* fixing persistenttextediting element which is used in a11y mode

* removing texteditingelement and using texteditingstrategy from hybridtextediting. fixing the unit tests. fixing comments

* fix unit tests

* add todos for firefox tests

* fixing chrome/android a11y issue

Author: nturgut

lib/web_ui/lib/src/engine/browser_detection.dart

@@ -29,10 +29,23 @@ enum BrowserEngine {
 /// Lazily initialized current browser engine.
 BrowserEngine _browserEngine;
 
+/// Override the value of [browserEngine].
+///
+/// Setting this to `null` lets [browserEngine] detect the browser that the
+/// app is running on.
+///
+/// This is intended to be used for testing and debugging only.
+BrowserEngine debugBrowserEngineOverride;
+
 /// Returns the [BrowserEngine] used by the current browser.
 ///
 /// This is used to implement browser-specific behavior.
-BrowserEngine get browserEngine => _browserEngine ??= _detectBrowserEngine();
+BrowserEngine get browserEngine {
+  if (debugBrowserEngineOverride != null) {
+    return debugBrowserEngineOverride;
+  }
+  return _browserEngine ??= _detectBrowserEngine();
+}
 
 BrowserEngine _detectBrowserEngine() {
   final String vendor = html.window.navigator.vendor;

lib/web_ui/lib/src/engine/text_editing/input_type.dart

@@ -66,7 +66,7 @@ abstract class EngineInputType {
   html.HtmlElement createDomElement() => html.InputElement();
 
   /// Given a [domElement], set attributes that are specific to this input type.
-  void configureDomElement(html.HtmlElement domElement) {
+  void configureInputMode(html.HtmlElement domElement) {
     if (inputmodeAttribute == null) {
       return;
     }