Replace private attributes with public resources.

The change replaces all existing usage of private resources in
SettingsLib with corresponding public resources. The only exception
is android:string/config_headlineFontFamily where there's no proper
replaccement.

The library is currently used by bundled apps (such as SettingsGoogle)
and unbundled apps (such as PermissionController and
CellBroadcastReceiver). Since we still want these bundled apps to
reference config_headlineFontFamily properly while not breaking
unbundled apps due to them referencing private attributes, we added a
new attribute settingslib_config_headlineFontFamily (alongside with
other FontFamily variance for completeness) in
SettingsTheme/res/values-v31/strings.xml which points to
config_headlineFontFamily by default. Then, in separate CLs, we will add
resource overrides to these unbundled apps to replace the value of
settingslib_config_headlineFontFamily to point to a public value. While
this means that the style of the pages from the unbundled apps will be
different from the rest of SettingsLib clients, the change provides a
tactical fix to make sure that these unbundled apps won't crash when
shipped to other devices. We can address the issue at its core by
potentially exposing some private resources in future Android releases.

Bug: 191387775
Bug: 190964071
Bug: 196106314
Test: manual test to confirm this is a no-op CL.
Change-Id: Ie25950d9f54964aa40038a27b302ed017e4e4d15