Optionally support accessibility with UiAutomator

Adding a flag to AccessibilityServiceInfo that only works
for UIAutomator that supresses other services. This flag
is set by default for UIAutomation to match the current
behavior, but tests may clear the flag and enable other
services.

Needed to improve cts coverage of AccessibilityService.

Bug: 26592034
Change-Id: Icfc2833c1bd6546a22a169008d88a6b15e83989c