Sync input transaction for startActivitySync

The method should be only used for tests. The tests usually expect
a stable state to proceed next step after the method returns.

By using syncInputTransactions(waitForAnimations=true), it can cover
both the purpose of [1] and [2].

[1]: Ifd7bfd41b39518518f4013fad80c3acd1e8b2354
[2]: I5457ab67ac574530dc1aa84549ca11e7e3f0d714

The original mEnterAnimationComplete is unable to handle trampoline
activities, i.e. the target activity launches another activity
in its onCreate. Then the target activity may not receive animation
complete or its onStop will clear the animation complete state, and
waitForEnterAnimationComplete doesn't know what's the next activity
to wait for. That always leads to a 5s timeout.

While syncInputTransactions can wait for global transition, so it can
return once the entire consecutive launch sequence is done.

Bug: 330043325
Flag: TEST_ONLY
Test: atest CtsWindowManagerDeviceActivity:ActivityLifecycleTests
Change-Id: Iea1e2840bbcb8dcde1a80340c4ae42e26ebf009a