This reverts commit 45844a3.

Reasons to revert:

* For full text selectable readonly editor contents, `SelectableText`
  only works on `TextSpan` children. `WidgetSpan` will make a gap for
  text selection and implementing a `SelectableWidgetSpan` combines both
  kinds of span is not easy to do: assert failure everywhere.
* `SelectableArea` handles `onTap` event where we only want
  the gesture passed to children so that users could activate reply
  state by a single tap, to fix the issue we need a custom ignore pointer
  widget.
* Rendered style not consists comparing the editor when editing and
  viewing page contents because the later one uses custom html parser
  while the former one uses editor which renders custom bbcode tags, they
  are not the same, both in history and in the future, as long as the
  process differs. And the html parser is quite limited and not stable,
  endless html layout rules are not clearly implemented, especially in
  line break. Frequently used layout are supported but not always be,
  massive special logic in the custom html parser makes it hard to
  maintain, let alone the selectable text feature we want to land in a
  future version. I think it's time to sunset the current html parser,
  or at least render into quill_delta so that we can have consistent
  contents appearance when editing and viewing contents.

Next step:

* Other implementation may not work, like use `Wrap` to simulate the
  original rich text features in flutter SDK, I don't think the result
  could be better than the one in SDK.
* We need selectable text and consistent appearance when editing and
  viewing contents so render it in the bbcode editor is the best choice.
  Waiting for upstream fix selection in readOnly mode here:
  singerdmx/flutter-quill#2529
  After that, parse supported tags here:
  https://github.com/realth000/tsdm_client/blob/81395ca8f5f5ee9ebe63cff1d223f585a895bf9a/lib/utils/html/html_muncher.dart#L335
  into custom bbcode tags to let the bbcode editor render it as common
  quill_delta tags, hard but worth it.

* master: (83 commits)
  Add copyWith methods to DefaultStyles, HorizontalSpacing, and VerticalSpacing (singerdmx#2550)
  docs: update migration guide to relfect singerdmx#2529
  chore(release): prepare to publish 11.4.0
  feat: allow to override link validation check, and accept mailto and other links by default (singerdmx#2525)
  chore(release): prepare to publish 11.3.0
  Fix selection in readOnly mode, Add magnifier via RawMagnifier widget (singerdmx#2529)
  Clarify platform support of QuillEditorConfig.onKeyPressed (singerdmx#2542)
  chore(release): prepare to publish 11.2.0
  feat: cache for toPlainText in Document to avoid unnecessary text computing (singerdmx#2482)
  chore(example): update deps
  chore(release): prepare to publish 11.1.2
  fix: QuillEditor doesn't respect the system keyboard brightness by default on iOS (singerdmx#2522)
  chore(release): prepare to publish flutter_quill_test
  chore(release): prepare to publish 11.1.1
  Chore: general improvements in flutter_quill_tests API (singerdmx#2512)
  Explicitly schedule frame on secondary click. (singerdmx#2507)
  chore(release): prepare to publish 11.1.0
  fix: unpredictable endless loop of '_handleFocusChanged' in the phase of page route changing when editor is set to readonly. (singerdmx#2488)
  feat: Enable BoxDecoration for DefaultTextBlockStyle of header Attribute (singerdmx#2438)
  Expose Rule type so that Document.setCustomRules can be used (singerdmx#2484)
  ...