Add withMerging

[felixfeng33]

Description
Currently, Slate lacks an API to merge a series of history records to the top of the stack. In some cases, the withMerging function is very useful, for example the upload status from pending to success and AI generate a series of text withMerging can make sure to remove it in one times redo.

Issue
Fixes: (link to issue)

Example
A GIF or video showing the old and new behaviors after this pull request is merged. Or a code sample showing the usage of a new API. (If you don't include this, your pull request will not be reviewed as quickly, because it's much too hard to figure out exactly what is going wrong, and it makes maintenance much harder.)

Context
If your change is non-trivial, please include a description of how the new logic works, and why you decided to solve it the way you did. (This is incredibly helpful so that reviewers don't have to guess your intentions based on the code, and without it your pull request will likely not be reviewed as quickly.)

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: 6df3336

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

This PR includes changesets to release 1 package

Name	Type
slate-history	Minor

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

[dylans]

This looks fine. Ideally we would add something to the docs as well, but I won't block the PR for that.