Fix wrong peek height of the notification panel

From N, the topmost notification slides in expanded from the top, not collapsed.
(https://android.googlesource.com/platform/frameworks/base/+/d1ad9ab3121cb54387c5d2b71b48708dcaed5c43)
But when peek from status bar, the peek height was measured with collapsed height.
Therefore fix the peek height with expanded height of the topmost notification.

Test: manual - Test peeking from status bar with expandable topmost notification.
Change-Id: I46173c9e82a1221b543133c38ec6aaf746244011
(cherry picked from commit c2ed273ca592e008917e74ad1f3ce9c9ccddd041)
(cherry picked from commit 09b798ab2041d792056a64562f73c8b11997b42e)