Synthetic target tweaks

- Just pass the app bounds for the synthetic target (so at least the
  bounds are valid)
- We should be sending the home task surface, and not the home task
  overlay surface

Bug: 366021931
Bug: 366022874
Test: atest WMShellUnitTests
Flag: EXEMPT bugfix
Change-Id: Id031024f53e03185f293b3689ef0742ea4b7b79d