This includes:
- Suggestion List: Check if a node exists to scroll into view.
- Autocomplete: reset state for empty text.
- Adds auxiliary class names for editor styles in the widgets editor.
- Extract snackbars into a separate component.
- Rich text: run input rules after composition end.
- iframe: load inline styles.
- Multi select: select all: restore ref callback.
- Writing flow: allow select all from empty selection.
- Post Excerpt: Fix excerpt_more filter conflict and remove wordCount attribute.
- Add the percent unit to the default units in Core.
Props desrosj, youknowriad.
Merges [51443] to the 5.8 branch.
Fixes#53397.
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