Make detachViewFromParent more robust

Calling detachViewFromParent() without calling remove or attach in the
same drawing frame could, in some situations, cause a crash in the native
DisplayList code. detach/attach are intended to be very lightweight and do
not manage the native DisplayList content the same way that add/remove do.
Nor do they cause an invalidate() or requestLayout(), which would cause the
native structures to get recreated appropriately.

This fix makes this process more robust in two ways:
- DisplayLists should not get finalized (therefore destroying their native
structures) when there are still parent DisplayLists referring to them
(each DisplayList keeps references to its child DisplayLists). This will
prevent the native crash associated with unmatched detach*() calls.
- The docs for detach/attach have been enhanced to make it easier for
developers to understand how to use these methods more correctly and
successfully.

Issue #7064818 detachViewFromParent() should be more robust

Change-Id: I53befc04d5d58c225060f397725566d470488c9b