Respect nav button tinting in SUW

* Check was originally added with rationale in
b/204384193#comment26, however presently we
do provide insets to SUW as of b/253538830
so looks like now we are getting the correct
info from SysUI
* There is a possibly related issue where buttons
are not tinted correctly on the final page of
SUW (b/265238238)

Test: Went through setup manually via adb
and observed that on light theme with dark
dialog scrim the button changes color
adb shell am start -a android.intent.action.MAIN -n com.google.android.setupwizard/.SetupWizardTestActivity
Bug: 256521774

Change-Id: I080033e21d22fbc366b7248b2d647fec610a5fb9