Fix sometime couldn't trigger A11y button with 3-finger

We inject the down events from where we detect the 3-finger swipe
gesture. It may not trigger the A11y Button if the event is not inside
the system gesture detection area.

We inject the original down location to injection all down events.

Bug: 166187595
Test: manually test
Change-Id: I0c0f84047fc24e40724332d51d7e3dc414bd0186