Use a better and simpler default name for multi-file archives

Now the default name of a multi-file archive created from the file actions plugin is the common prefix of those file's filename or "Archive.[extension]", if they don't match, instead of "[name of parent folder].[extension]".

"Screenshot_123.jpg", "Screenshot_1234.jpg" => "Screenshot_123.[extension]"
"cats.jpg", "dogs.jpg" => "Archive.[extension]"

Example for multiple screenshot files: Screenshot_20220210_075625

CCBUG: 446728

cc @ngraham
superseeds !96 (closed) Replaces !98 (closed)

Edited by Méven Car

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