Check for selection in ve.ce.Surface#onDocumentFocus

Instead of checking if focus was caused by a mouse event, check if there
is a selection already.

This seems to work correctly both on desktop and iOS Safari.

Bug: 66697
Change-Id: Ief6c44cb6c5e25ccdff01f632a5f65a8abc4f3ed
Merge "Check for selection in ve.ce.Surface#onDocumentFocus"