Introduce setSplashscreenStyle to specify splash screen style.

Provide a method ActivityOptions#setSplashscreenStyle to specify
splash screen style if needed.

If not set, the default option will be empty-style splash screen, so
without any other change, the activity launched from systemui with
ActivityOptions will become empty style splash screen.

Bug: 188023621
Bug: 189293785

Test: manual test start application from Launcher and Notification.

Change-Id: I299320db8f32fbd835c7ec0acaad3df3486a13f5