[web:tests] switch to new HTML DOM matcher (#52354)

Remove the over-architected and under-utilized `canonicalizeHtml` and `HtmlComparisonMode`. Replace with a new `hasHtml` matcher.

The new matcher produces considerably better error messages when matching fails (see `matchers_test.dart` for multiple examples). It also allows focusing on particular parts of the DOM rather than looking for a full match. This way a test can test just the functionality it cares about, and it can skip specifying what unrelated parts should look like (i.e. it prevents over-testing). For example, let's say you want to test that an `<flt-semantics>` element has an `aria-label` attribute. You can use a DOM pattern that specified just that:

```
expect(
  element,
  hasHtml('<flt-semantics aria-label="hello"></flt-semantics>'),
)
```

This will check for the existence of `<flt-semantics>` and `aria-label="hello"`. It will ignore everything else that's unrelated to ARIA labels. For example, the element may have its geometry specified in the `style` attribute, an `id` attribute, and many other things, but if the test doesn't care, it doesn't need to specify those things (it can, if needs to though). This also applies to `style` properties. See more examples in the `matchers_test.dart` file.

Author: yjbanov

lib/web_ui/lib/src/engine/dom.dart

@@ -597,9 +597,9 @@ extension DomElementExtension on DomElement {
   external set _id(JSString id);
   set id(String id) => _id = id.toJS;
 
-  @JS('innerHtml')
-  external set _innerHtml(JSString? html);
-  set innerHtml(String? html) => _innerHtml = html?.toJS;
+  @JS('innerHTML')
+  external set _innerHTML(JSString? html);
+  set innerHTML(String? html) => _innerHTML = html?.toJS;
 
   @JS('outerHTML')
   external JSString? get _outerHTML;