WIP: Update Clear-Host on UNIX to also clear the scrollback buffer

[SteveL-MSFT]

PR Summary

Clear-Host currently uses the clear command to clear the screen. However, that merely clears what is on the visible screen and not the entire buffer. This is a difference in behavior with Windows which also clears the scrollback buffer. Fix is to output the ESC[3J CSI sequence to clear the scrollback buffer.

cc @mklement0

Fix #8554

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[SteveL-MSFT]

Marking this as WIP waiting on Committee review of the issue

[mklement0]

Thanks, @SteveL-MSFT. What is missing is the proposed removal of the clear alias on Unix-like (non-Windows) platforms.

[SteveL-MSFT]

Closing this due to @PowerShell/powershell-committee decision