Fix screenshot preview accessibility label

Changes label to match the "Edit" button. Also makes the description
more correct when the preview is /not/ tappable (i.e. when the
screenshot was taken, but we haven't successfully saved it to disk
yet).

Test: manual
Fixes: 152834239
Change-Id: Iae406bcc672e56445e620349851e94cfaf97859a
2 files changed