Fix child element decorations

[jasonphillips]

Description
Due to a regression, decorations that cross child elements were not properly passed to those elements for rendering; the offsets from the anchor and node were being applied to every child node, rather than the specific intersection. This PR ensures that the child elements always receive the intersecting range of the decoration.

Issue
Fixes: #4909

Example
Given this value, where some elments are nested under a parent element:

[
  {
    type: "parent",
    children: [
      { type: "block", children: [{ text: "foo" }] },
      { type: "block", children: [{ text: "bar" }] },
      { type: "block", children: [{ text: "baz" }] }
    ]
  }
]

And this return from decorateNode on the parent element above:

[
    {
        anchor: { path: [0, 1, 0], offset: 1 },  // from b(ar
        focus: { path: [0, 2, 0], offset: 2 },   // to ba)z
        bold: true
    }
]

The decorations passed down to the child elements will be only their intersecting range, so that the decoration is applied correctly across the children.

From the linked issue, see this image of the regression (this PR seeks to restore prior behavior shown on 0.66 here):

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: 898cd87

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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[BitPhinix]

🚀

[jasonphillips]

The regression I'm fixing was caused by #4876 - which I should have tagged above for context.

[nemanja-tosic]

Good catch, and good PR.

I've left a couple of questions for consideration, and also if you could as part of this PR please remove const decorate = useDecorate() on line 36 (and the import for useDecorate) as it's not used anymore.