feat: add edit and tabnew to win_split_mode

[pirey]

Summary

Add tabnew and edit to win_split_mode option.

Related Issues

Related #398

Changes

• added tabnew and edit to win_split_mode enum in _meta.lua

Checklist

I confirm that I have:

• Followed the
  Conventional Commits
  specification (e.g., feat: add new feature, fix: correct bug,
  docs: update documentation).
• My PR title also follows the conventional commits specification.
• Updated relevant documentation, if necessary.
• Thoroughly tested my changes.
• Added tests (if applicable) and verified existing tests pass with
  make test.
• Checked for breaking changes and documented them, if any.