Reparent task before setting always on top

Always on top does not work for nested tasks.
Make sure task is reparented before setting it to always on top.

Bug: 396313972
Test: atest WMShellUnitTests:BubbleUtilsTest
Flag: com.android.wm.shell.enable_create_any_bubble
Change-Id: Ia0b421a70403e2dd853b4695032c2c742ecbcc68