20e2de3a37
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.