Fix NODE_TO_KEY correction for split_node and merge_node

[bryanph]

Description
Fixes #4900

Issue
Fixes: #4900

Example
The logic in with-react was not resetting the node keys for the right nodes for split_node and merge_node operations. This fixes that so that on split_node the node being split does not get remounted and on merge_node the node being merged into also does not get remounted.

Context
See #4900

Checks

• The new code matches the existing patterns and styles.
• The tests pass with yarn test.
• The linter passes with yarn lint. (Fix errors with yarn fix.)
• The relevant examples still work. (Run examples with yarn start.)
• You've added a changeset if changing functionality. (Add one with yarn changeset add.)

[changeset-bot]

🦋 Changeset detected

Latest commit: c242b0a

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

This PR includes changesets to release 1 package

Name	Type
slate-react	Patch

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[dylans]

Thanks! I’d love to see a test for this though I know that’s not easy yet. Please add a changeset when you get a chance.

[bryanph]

@dylans yeah a test here would be nice indeed, will see what I can do. For a test I'd have to check whether a component remounted or not, I don't think cypress can do that. Or can go more basic and test the matches array returned here is correct for some cases.

[nemanja-tosic]

@bryanph don't know about cypress, but here's a react test renderer version that fails against previous version but works with the PR:

it('should not unmount', async () => {
  const editor = withReact(createEditor())
  const value = [{ children: [{ text: 'hello' }] }]
  const mounts = jest.fn<void, [Element]>()

  let el: ReactTestRenderer

  act(() => {
    el = create(
      <Slate editor={editor} value={value} onChange={() => {}}>
        <DefaultEditable
          renderElement={({ element, children }) => {
            useEffect(() => mounts(element), [])

            return children
          }}
        />
      </Slate>,
      { createNodeMock }
    )
  })

  // slate updates at next tick, so we need this to be async
  await act(async () =>
    Transforms.splitNodes(editor, { at: { path: [0, 0], offset: 2 } })
  )

  expect(mounts).toHaveBeenCalledTimes(2)

  // TODO: assertion against something specific to elements
})

[bryanph]

@nemanja-tosic awesome, thanks! I pushed two tests for the particular cases being fixed here based on your example here. Let me know if there's something else I can assert here.