Make carrier text update on theme change

Previously, the colors did not update because the background was
a fixed black. Now that background blur is enabled, the font color
needs to update with the theme/mode like the QS tile fonts.

Bug: 405266952
Flag: com.android.systemui.shade_header_font_update
Test: ran affected tests; manually verified
Change-Id: I4b266d5ca3ca440818ef951b6868e35cb2cb4865