[SettingsProvider] enforce @Readable for getAll*Settings methods

BUG: 208268457
Test: atest android.appsecurity.cts.ReadableSettingsFieldsTest
Change-Id: If2512b0b7586d755104c69736c500dffde860cda
Merged-In: If2512b0b7586d755104c69736c500dffde860cda
1 file changed