[SB] Small reorganization of text styles for status bar.

Creates a new "TextAppearance.StatusBar.Default" style that has the new
fonts, and then has the clock text style extend from that default style.

This also updates the carrier text on keyguard to use the new fonts.

Bug: 393609116
Flag: com.android.systemui.status_bar_font_updates
Test: Verify fonts of clock, carrier text, and battery estimate
Change-Id: I46b2cc1b9e5a742d70edc29b0686cc325da1e232