Fix: revert to prior decorations behavior

[jasonphillips]

Description
This reverts #4876 (and the related #4910 fix to it) while we seek out another way of improving decorations to meet everyone's needs without regressions.

Context
See: #4993

One great addition from #4876 which was not fully reverted here is the creation of tests for slate-react. The specific decorations tests themselves were removed--while the ideal behavior of decorations continues to be revisited in future PRs, and then we can restore them--but the test setup itself was kept, particularly since at least one subsequent PR also uses it.

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: e2e3df8

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

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR