[sts] add @SecurityTest for testing invalid font size scales BUG: 175816890 Test: sts-tf > run sts-engbuild-no-spl-lock -m CtsProviderTestCases -t android.provider.cts.settings.Settings_SystemTest#testSystemSettingsRejectInvalidFontSizeScale Change-Id: I7bdfbccf28f99084230068b388fea94e21892e55 (cherry picked from commit 493d5913313dfb6b64868de4c4720e5d0b82771f) Merged-In: I7bdfbccf28f99084230068b388fea94e21892e55