Documents List: use multiple-files Save dialog

[Yaron10]

STR:
Have 3 files opened: 1 saved and 2 unsaved.
Open the Documents List.
Select the 2 unsaved files, right-click and Close Selected Files.

Result:
The single-file Save dialog is displayed twice (once for each unsaved file).

Expected:
The multiple-files Save dialog should be displayed once for all unsaved files.

Ref: #13761 (comment).

(Relevant to Close Other Files as well).

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@donho,

Could you please look into it?
Thank you.

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