[Notif redesign] Update text style in guts priority btn

Update the font and color of text in the guts priority option based on
the design spec. Also update the associated icon color accordingly.

Bug: 394822197
Bug: 409496809
Flag: android.app.notifications_redesign_fonts
Test: manual
Change-Id: I4991b410ce8cc861905293c1870164fff633cc48