Expose the Side by side horizontal mode in save dialog options.

Stereo type can be used using --stereo-type=SplitviewportHorizontal
but the save screenshots and save animation dialogs did not
allow to choose this stereo mode.
This mode as been added in those 2 dialogs.

Change-Id: I5965bf517abab2722ae9397e71a6f105d3a913f7
Merge topic 'AddSideBySideHorizStereoModeToSaveDialogs' into next

a38fba8b Expose the Side by side horizontal mode in save dialog options.