Use desktop task's custom density for its window decor

When tasks are launched or moved to Desktop, a custom density is applied
to them that is different from the rest of SystemUI. With this change,
the task's window decoration will also use that same custom density to
prevent misalignment when a custom caption bar is being drawn by the
system and app.

Flag: com.android.window.flags.enable_app_header_with_task_density
Bug: 332414819
Test: enter desktop, observe caption bar density matches app content
Change-Id: I223fdd443f7ca7fb16092e7b2b94407c0cb4e62d