Introduce files.maxMemoryForClosedFilesUndoStackMB

[alexdima]

This PR adds a new setting files.maxMemoryForClosedFilesUndoStackMB.

• It fixes Introduce a memory limit to saved undo-redo elements. #93687 because now there is a hard upper bound to the amount of memory consumed for the undo stacks of closed files.
• It fixes Settings for Disabled Persisted Undo #94778 because the setting can be configured "files.maxMemoryForClosedFilesUndoStackMB": 0 which effectively disables the feature.
• It fixes Intrusive "Keep the undo-redock stack" dialog on tab close #95970 because undo stacks above the upper bound are never saved and if the upper bound is reached, the oldest undo stacks are dropped, thus there is no more need for the prompt, which is now removed.

[hd-esteban]

how can I set it to zero?

[alexdima]

The new setting is now files.restoreUndoStack which can be set to true or false.