[Media TTT] Define a chip controller and a way to issue commands via adb

to control the chip.

(To test, you will need to issue the command `adb shell am broadcast -a
com.android.systemui.action.SET_FLAG --ei id 900 --ez value 1` in order
to enable any media TTT code.)

Bug: 203800327
Test: `adb shell cmd statusbar media-ttt-chip-add` displays the chip
Test: `adb shell cmd statusbar media-ttt-chip-remove` removes the chip
Test: atest MediaTttChipControllerTest
Change-Id: Ib404206d0a0bdcbc8e2d1c9ddedbbe7c63dcd91e