Add Unit tests for System Shortcut.

Update SystemShortcut<T extends ActivityContext> and remove dependency on Launcher so we can write unit tests.

Introduce TestSandboxModelContextWrapper , wrapper around SandboxModelContext and ActivityContext.

Use SandboxModelContext for testing since we need UserCache, AllAppsContainerView, AllAppsStore to be spied and verified for function calls.

StatsLogManager is not verified in this cl, We can do as follow up.

Bug: 319250810
Test: Manual.
Flag: aconfig com.android.launcher3.enable_private_space TEAMFOOD

Change-Id: If767128a502e40d2016a331db4a342f20f24c588