Extend the `manualRowResize` plugin with a method allowing to retrieve the last desired row height.

[jansiegel]

Context

This PR extends the manualRowResize plugin with a method that retrieves the row height value from the last attempt at manually changing the row height (even if the actual row height didn't change, because of the nature of the TD elements).

How has this been tested?

Added a test case.

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature or improvement (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Additional language file or change to the existing one (translations)

Related issue(s):

1. handsontable/dev-handsontable#1868

Affected project(s):

• [x] handsontable
• [ ] @handsontable/angular
• [ ] @handsontable/react
• [ ] @handsontable/vue
• [ ] @handsontable/vue3

Checklist:

• [x] I have reviewed the guidelines about Contributing to Handsontable and I confirm that my code follows the code style of this project.
• [x] I have signed the Contributor License Agreement
• [ ] My change requires a change to the documentation.

[github-actions[bot]]

Launch the local version of documentation by running:

npm run docs:review 51ed1e729cfed5a0f12f04ee855f45da25bff233