Respect locale direction in TimePicker AM/PM location

Previously, the code that decided where the AM/PM indicator should
end up relative to the hours and minutes assumed that the locale was
LTR. Now it works correctly for RTL locales too.

Bug: 62846484
Test: manual (tested adding an alarm under ar-EG, en-US, and ta-IN, all of which are 12-hour)
Change-Id: I748baff01e2b3398747a2f8c074edbd16322bdf9