Make the PipManager remember custom aspect ratios

Currently, the PipManager always reverts any pip window to the
preconfigured default size and position after any movement (e.g. pip
menu dismissal, or keyboard dismissal).

This does not take into account that a specific aspect ratio might have
been set in the PictureInPictureParams.

This change leverages the already correct calculation from the
PipBoundsHandler to update the default and current pip bounds kept by
the PipManager.

Bug: 163787014
Test: atest CtsSystemUiTestCases:BasicPipTests
Change-Id: I74829d95bc3ef06e6962020d5a56998128ec3640