Images: use first alignment, but last size and caption.

Note that we don't wt2wt cleanly when multiple conflicting options are
present; we drop all but the active one.

Failing selser tests are false reports because of wt2wt failures -- 
selser output is correct.

Bug: 48664
Change-Id: I11d27e61f47630861231f72be8328236a9968adc
Merge "Images: use first alignment, but last size and caption."