fixed format on save not always being done

[teslae1]

What this PR does / why we need it:
Fixes format on save problem.
I was able to reproduce the problem using the video from the issue,
but also found a more reliable way of reproducing it:

• create a file that needs formatting on disk
• open the file in vscode
• have the 'editor.formatOnSave' setting toggled
• without changing any text of the file do ':w'
• won't format
• do ctrl + s
• will do format

The problem is that vscode won't do format on save when calling 'vimState.document.save()' if the textual contents is no different from disk (document not 'dirty').

Which issue(s) this PR fixes
#9883

[J-Fields]

Thanks!