Shift+Tab on first field of entry editor should focus last field of previous tab

[koppor]

#13938 introduced the functionality to Tab through all fields of the entry editor.

There should be the inverse functionality: Shift+Tab should focus the previous field - and if there is no previous field on the current entry editor tab, focus the previous tab and the last field.

Code can get inspirations from #13938.

[CXZHANG0508]

/assign-me

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