Update hex numbers in Accessibility code to use bit shift

This CL updates hex numbers in the accessibility
code to use bit shifts instead, as the newer and
preferred method going forward.

It also adds missing comments.

There are no functional changes with this CL.

Bug: 253134477
Test: No functional changes, existing tests.

Change-Id: I507b5eeb31570e417b5753683d8ab00db1c3d551