Base Manage Windows header position on task coordinates.

For freeform tasks, the manage windows menu was using captionX /
captionY values, which are both 0. This CL changes it to task left/top.

Bug: 380268041
Test: Manual
Flag: EXEMPT bugfix
Change-Id: Ib405e11dc2d67ae2c86fcf5e4058c93df3954c4a