Use WUC Backdrop instead of SystemBackdrop

DWMWA_SYSTEMBACKDROP_TYPE or DWMWA_USE_IMMERSIVE_DARK_MODE require only
a top level window. Additionally, DWMWA_SYSTEMBACKDROP_TYPE is only
available on WIN11_22H2+. To make the experience consistent between all
platform versions where the redirection bitmap will be removed, as well
as across top level and child hwnds, only use the WUC Backdrop as the
window backdrop.

Additionally, this change ensures that the WUC Backdrop only gets added
when the Mica titlebar is not being used.

Bug: 415385215
Change-Id: I3760e6563deb6c16c19f3005c246ae0d810bdf4c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6512200
Reviewed-by: Mike Wasserman <msw@chromium.org>
Commit-Queue: Sahir Vellani <sahir.vellani@microsoft.com>
Cr-Commit-Position: refs/heads/main@{#1459754}