Blender Git Loki

Fix T72803: Texture Paint: Shortcut 'Shift + S' Does Not Save an Image

'Shift + S' is taken by toggeling Smooth Stroke in the keymap, should be
'Shift + Alt + S' (this also goes more in line with other editors, where
Alt is added to the shortcut used by 'Save' to do 'Save As')

Maniphest Tasks: T72803

Differential Revision: https://developer.blender.org/D6572