Make it possible to disable Accessibility checks

[vaughandroid]

As far as I can tell, it isn't possible to disable the accessibility checks once they are enabled. This makes it impossible to use for a subset of tests.

Adding a method like AccessibilityChecks.disable() would make it possible to add the accessibility checks to cover specific tests, rather than the whole suite.

[caseyburkhardt]

Yes, we should have exposed a disable() on AccessibilityChecks. Will look into it.

As a workaround for now, give this a shot:
ViewActions.removeGlobalAssertion(AccessibilityChecks.accessibilityAssertion());

[vaughandroid]

Finally got around to trying to build a TestRule using this workaround. It doesn't work, since AccessibilityChecks.checksEnabled doesn't get reset. I've hacked it for now with reflection.

For anyone else who runs into this, it looks like the commit here fixes it in AndroidX: android/android-test@ac49334

[caseyburkhardt]

Resolved by this change.