Fix two panel accessibility issues

When two panel home was enabled in Launcher the items on
the left panel weren't able to get selected while on Talkback
because of an incorrect calculation in getScrollProgress.
Also the user was unable to jump to other workspaces by doing
simple one finger swipes because the page jump count was
only 1.

Test: manual
Bug: 174464170
Change-Id: I6cfe39b5059e8e7e7a32c9b0d372c658e796c3e8