docs: Updated descriptions of device orientation angles.

Given recent reversal of "roll" definition (positive angles now
represent counter-clockwise rotation), updated the description for
this and the other orientation angles. Also updated explanatory text
and code samples within the "Position Sensors" page to reflect the
recent deprecation of STRING_TYPE_ORIENTATION.

Bug: 23822069
Change-Id: I083a55011ea41c4a6533b78ee38a32479310f4cf