Add menu and media play/pause global actions [1/2]

Accessibility services in Android currently don’t have the ability to
invoke the menu on the device. Furthermore, although they have access
to a play/pause media API, they don’t have the ability to inject the
media play/pause key event on a device, which can affect the experience
for users with disabilities as underlying apps may have special case
handling for this key.

This change involves adding two global actions, GLOBAL_ACTION_MENU and
GLOBAL_ACTION_MEDIA_PLAY_PAUSE, to AccessibilityService, and
their respective system actions.

Test: manual
Steps:
1. Build the images and flash to device
2. Ensure that menu is invoked on screen when GLOBAL_ACTION_MENU
global action is performed
3. Ensure that media can be played & paused when
GLOBAL_ACTION_MEDIA_PLAY_PAUSE global action is performed

Flag: ACONFIG android.view.accessibility.global_action_menu DEVELOPMENT

Flag: ACONFIG android.view.accessibility.global_action_media_play_pause DEVELOPMENT

Bug: 334954140

Change-Id: I84acc0516dfec90d73284b6a40ecaf36b7efad32