Maintain focus after column collapsing

[budnix]

Context

The PR changes make the focused cell always visible after the column collapsing.

If the current selection becomes collapsed, the focus is moved to the first visible column to the right. If no visible columns exist on the right, it's moved to the first column on the left (relative to the original focus position). If neither the right nor left columns are visible. The focus is never hidden.

How has this been tested?

I tested the changes locally, and I covered the fix with new tests.

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Related issue(s):

1. fixes https://github.com/handsontable/dev-handsontable/issues/1750

Affected project(s):

• handsontable

Checklist:

• I have reviewed the guidelines about Contributing to Handsontable and I confirm that my code follows the code style of this project.
• I have signed the Contributor License Agreement

[github-actions]

Launch the local version of documentation by running:

npm run docs:review a749ba9c80079f8f12674406928d4db1ba16a3dd