Refactor usage of clipboard

[springcomp]

PR Summary

While working on various upcoming PRs (notably #1674 and #584) I noticed this would be easier if some code cleanup/refactoring had taken place before,

I noticed a common pattern while trying to remove some text while supporting undo:

_singleton.SaveToClipboard(start, count, instigator, arg);
_singleton.SaveEditItem(start, count, EditItemCreate(_clipboard, start, instigator, arg));
_singleton.Remove(position, length);

Therefore, this PR introduces a new method to promote this pattern and refactors all ocurrences to use the new method.
While doing so, I also slightly refactor one or two obvious related changes to the clipboard handling.

PR Checklist

• PR has a meaningful title
  • Use the present tense and imperative mood when describing your changes
• Summarized changes
• Make sure you've added one or more new tests
• Make sure you've tested these changes in terminals that PowerShell is commonly used in (i.e. conhost.exe, Windows Terminal, Visual Studio Code Integrated Terminal, etc.)
• User-facing changes
  • Not Applicable

Microsoft Reviewers: Open in CodeFlow

[daxian-dbw]

Thanks for the refactoring, look mostly good to me, with a few comments.

[springcomp]

@daxian-dbw I believe I have addressed all feedback.
Please, would you re-review?

[daxian-dbw]

LGTM. I will help resolve the conflict.

[ghost]

🎉 v2.2.0-beta2 has been released which incorporates this pull request. 🎉