Fixes positioning issues with the bubble stack.

- Waits for layout before moving the stack to the initial position, so that width/height are correct. This was not caught by tests because the TestablePhysicsAnimationLayout posts all of its controller dispatch methods to a Handler, which caused them to wait for layout only in the tests. This seems unavoidable, unfortunately.
- Uses the status bar height resource value, rather than top inset, which is actually always zero.

Test: atest SystemUITests
Bug: 123635140
Change-Id: I2357445a7b1ab374e3a835884639e3b227207de3