Add configuration.assetsSeq check to equalsForTaskOrganizer

so that changing the system theme color triggers a onTaskInfoChanged
call. This will allow app headers (specifically for Wallpaper & Style
page in Settings app) to update its color accordingly.

This CL also removes a workaround that was added in
I1ebabd7e16d0fa4a71f889564781d28b1b303596 for the Settings page
mentioned above.

This CL also sets windowDecorationViewHolder to null in
CaptionController#releaseViews for WindowDecor2, so that the header gets
reinflated appropriately.

Fixes: 437224867
Bug: 412489198
Flag: EXEMPT bugfix
Test: atest WMShellUnitTests:com.android.wm.shell.windowdecor
Test: Manual - navigate to Wallpaper & Style in Settings > change the
Home screen color > observe that the header changes color along with the
app content. Test with enable_window_decoration_refactor flag off and
on.

Change-Id: I770db40d8c76ad3faa1ca238a9e0c79436a2bb17