fix(forms): refresh CodeMirror when MarkdownEditor becomes visible (#20239)

* fix(forms): refresh CodeMirror when MarkdownEditor becomes visible

* Restore `#20134` state sync fix and only refresh on the hidden-to-visible transition

- Reinstates the current `4.x` change handler and state watcher, which were
  accidentally reverted when this patch was authored against an older copy of
  `markdown-editor.js`.
- Keeps the `ResizeObserver` and `IntersectionObserver` connected for the whole
  lifecycle of the editor, since the state may change while it is hidden and it
  can be revealed again, but only calls `refresh()` when the editor transitions
  from hidden to visible instead of on every resize or scroll.
- Detects visibility using both `offsetParent` (inactive tabs use
  `display: none`) and computed `visibility` (collapsed sections hide content
  with `visibility: hidden`).
- Rebuilds the dist output against the latest `4.x`, resolving the merge
  conflict.

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Co-authored-by: Dan Harrin <git@danharrin.com>

Author: hamdyelbatal122