[Settings] keys with @TestApi need to have @Readable

This allows them to be accessed by test apps.

BUG: 183223092
Test: atest CtsAppSecurityHostTestCases:android.appsecurity.cts.ReadableSettingsFieldsTest#testSecurePublicSettingsKeysAreReadable
Change-Id: I2bdcab2d9279f5ef944b17896c7b31b84ca8dc81
1 file changed