Add a RTT setting in A11y screen

- Add RTT setting in Accessibility screen.
- Create a controller for RTT setting preference.
- Create an array strings to define the subtext.

Test: Rebuild, and visual
Change-Id: I248654c822284473b8a8265de4a3938af89cdf7a
Merged-In: I248654c822284473b8a8265de4a3938af89cdf7a
Fix: 146540478