Introduce SystemUIDialogFactory to create (Compose) SystemUIDialogs

This CL introduces SystemUIDialogFactory and ComponentSystemUIDialog to
easily create a SystemUIDialog whose content can then be set and whose
lifecycle can be observed. This way, people don't have to extend
SystemUIDialog all the time and we can very easily create dialogs with
custom content. The lifecycle and implementation of
SavedStateRegistryOwner is also required to set a Compose content on the
dialog. The implementation of ComponentSystemUIDialog was forked
directly from AndroidX ComponentDialog (http://shortn/_Fn58HvXtUt), with
the notable exception of onStop() that is slightly different than the
original (see the TODO there and b/296180426).

I then added an extension function on SystemUIDialogFactory to create a
SystemUIDialog with a Compose content. Note that the background of the
dialog is still drawn on the DecorView (like all SystemUIDialogs), but
the content itself is all drawn by Compose. That way, Compose dialogs
automatically play nicely with (Activity|Dialog)LaunchAnimator. I also
provide an AlertDialogContent to be used together with this extension
function to create simple dialogs with title, icon (optional), content
and buttons (optional).

This CL also updates the colors of the PlatformButtons to match the new
colors in the View system that were recently updated in
http://ag/23711768.

See b/283817398#comment6 for a video and screenshots.

Bug: 283817398
Test: atest ComposeDialogScreenshotTest
Change-Id: I537f77a2be639d6d97b247ae8d8d9ca5ec0214c3