Move whole lines as blocks when dragging or cutting

[dylans]

Fixes #5376

Dragging or cutting a selection that runs from the start of one line to the start of the next copies the line break, but the delete unhung the range and left the emptied block behind. Each move grew the document by one empty line.

The first version of this PR deleted with hanging: true. That merged containers: a cell drag removed a table cell, the paragraph after a list was pulled into the list, and the block after a dragged heading became a heading. This version decides per range:

Range	Copied fragment	Delete
Start of a top-level block to the start of a later one	hanging, with the line break	remove those blocks outright, no merge
Anything else (list items, table cells, partial lines)	unhung	editor.deleteFragment, as main does for cut

Also:

• Drag and cut share one path: the drop deletes through editor.deleteFragment (as cut already did), so plugins that guard deletion cover both.
• Tables example: uses that hook to clear a cross-cell selection cell by cell instead of merging cells. Core can't know about cells, so this lives in the example.
• Drop onto own selection: dropping text back onto its own selection is a no-op.

Tests:

• packages/slate-react/test/move-range.spec.ts (13 cases): plain lines, backward selections, headings, quotes, several lines at once, empty lines, a non-hanging range, an inline start, list items, a list followed by a paragraph, table cells, table rows, and the deleteFragment hook.
• Playwright drag tests run in Firefox only (the one engine that performs native text drags under Playwright); cut tests run in all browsers. They cover plaintext (drag a line, drop onto itself, cut a line), richtext (drag the quote line) and tables (drag between cells, cut across cells).
• Every new Playwright test fails on main except the drop-onto-itself guard, which main already handles. The full integration suite passes locally (179 passed), as do the strict checks on Node 24.

Known limit: nested moves leave the emptied list item or cell in place (main does the same), because removing it can't be done generically without breaking tables.

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🦋 Changeset detected

Latest commit: f141316

The changes in this PR will be included in the next version bump.

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slate-react	Patch

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[dylans]

Moving this back to draft. hanging: true fixes plain blocks and sibling list items, but in nested structures it merges containers. In a table, dragging from the start of one cell to the start of the next removes the second cell, leaving the row one cell short. Dragging the last list item up to the paragraph after the list pulls that paragraph into the list. Main only empties the first cell or item in those cases. I'll rework this so the deleted range matches the dragged fragment without merging across containers.