[flutter_html_iframe] Fix compile error in Flutter 3.32.0

- correct conditional imports: use dart.library.js_interop instead of dart.library.html
- remove ui_fake classes, it is legacy implementation and should be replaced by web_ui package

This is from an Open PR:
Sub6Resources#1485

Author: chillbrodev

packages/flutter_html_iframe/lib/flutter_html_iframe.dart

@@ -6,14 +6,12 @@ import 'package:webview_flutter/webview_flutter.dart';
 
 import 'iframe_unsupported.dart'
     if (dart.library.io) 'iframe_mobile.dart'
-    if (dart.library.html) 'iframe_web.dart';
+    if (dart.library.js_interop) 'iframe_web.dart';
 
 class IframeHtmlExtension extends HtmlExtension {
   final NavigationDelegate? navigationDelegate;
 
-  const IframeHtmlExtension({
-    this.navigationDelegate,
-  });
+  const IframeHtmlExtension({this.navigationDelegate});
 
   @override
   Set<String> get supportedTags => {"iframe"};

packages/flutter_html_iframe/lib/iframe_web.dart

@@ -1,11 +1,9 @@
 import 'dart:convert';
 import 'dart:math';
+import 'dart:ui_web' as ui_web;
 
 import 'package:flutter/material.dart';
 import 'package:flutter_html/flutter_html.dart';
-import 'package:flutter_html_iframe/shims/dart_ui.dart' as ui;
-// ignore: avoid_web_libraries_in_flutter
-import 'dart:html' as html;
 
 import 'package:webview_flutter/webview_flutter.dart';
 
@@ -21,34 +19,38 @@ class IframeWidget extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    final givenWidth =
-        double.tryParse(extensionContext.attributes['width'] ?? "");
-    final givenHeight =
-        double.tryParse(extensionContext.attributes['height'] ?? "");
+    final givenWidth = double.tryParse(
+      extensionContext.attributes['width'] ?? "",
+    );
+    final givenHeight = double.tryParse(
+      extensionContext.attributes['height'] ?? "",
+    );
     final html.IFrameElement iframe = html.IFrameElement()
       ..width = (givenWidth ?? (givenHeight ?? 150) * 2).toString()
       ..height = (givenHeight ?? (givenWidth ?? 300) / 2).toString()
       ..src = extensionContext.attributes['src']
       ..style.border = 'none';
     final String createdViewId = _getRandString(10);
-    ui.platformViewRegistry
-        .registerViewFactory(createdViewId, (int viewId) => iframe);
+    ui_web.platformViewRegistry.registerViewFactory(
+      createdViewId,
+      (int viewId) => iframe,
+    );
     return SizedBox(
-      width: double.tryParse(extensionContext.attributes['width'] ?? "") ??
+      width:
+          double.tryParse(extensionContext.attributes['width'] ?? "") ??
           (double.tryParse(extensionContext.attributes['height'] ?? "") ??
                   150) *
               2,
-      height: double.tryParse(extensionContext.attributes['height'] ?? "") ??
+      height:
+          double.tryParse(extensionContext.attributes['height'] ?? "") ??
           (double.tryParse(extensionContext.attributes['width'] ?? "") ?? 300) /
               2,
       child: CssBoxWidget(
         style: extensionContext.styledElement!.style,
         childIsReplaced: true,
         child: Directionality(
           textDirection: extensionContext.styledElement!.style.direction!,
-          child: HtmlElementView(
-            viewType: createdViewId,
-          ),
+          child: HtmlElementView(viewType: createdViewId),
         ),
       ),
     );