Do not allow apps having shared uid with system to access VD settings

Apps such as Settings have shared uid with system_server, so
SettingsProvider allows them to access device-aware settings.
This change fixes that by putting an additonal check for
package name.

Test: atest SettingsProviderTest
Fixes: 436181324
Flag: android.companion.virtualdevice.flags.device_aware_settings_override
Change-Id: Ie9138e4fc133bc43cb817d4f238208bc5194c960