Correct reversed visual block mode navigation

[KyleBarton]

Partially addresses #27385

One problem with visual block mode in vim is that it doesn't properly handle the up or down commands when the selection is reversed - e.g. when the cursor lies at the beginning of the text, rather than the end:

Screen.Recording.2025-03-27.at.9.25.29.AM.mov

Screen.Recording.2025-03-27.at.9.26.06.AM.mov

This change fixes this so that boxes can be drawn down and to the left and up and to the left:

Screen.Recording.2025-03-27.at.9.27.51.AM.mov

Release Notes:

• Improved visual block mode when cursor is at beginning of selection

[cla-bot]

Thank you for your pull request and welcome to our community. We could not parse the GitHub identity of the following contributors: Kyles IC Macbook.
This is most likely caused by a git client misconfiguration; please make sure to:

1. check if your git client is configured with an email to sign commits git config --list | grep email
2. If not, set it up using git config --global user.email email@example.com
3. Make sure that the git commit email is configured in your GitHub account settings, see https://github.com/settings/emails

[cla-bot]

Thank you for your pull request and welcome to our community. We could not parse the GitHub identity of the following contributors: Kyles IC Macbook.
This is most likely caused by a git client misconfiguration; please make sure to:

1. check if your git client is configured with an email to sign commits git config --list | grep email
2. If not, set it up using git config --global user.email email@example.com
3. Make sure that the git commit email is configured in your GitHub account settings, see https://github.com/settings/emails

[KyleBarton]

I'm closing and re-opening with a new PR - apologies, my git config was wrong and I needed to fix it.