Allow WPS to create windows with multiple type

Before WindowProviderService, Service can add windows with several
window types. This is previously not allowed for WindowProviderService
because a context can only associate with a window container.
However, it may cause regressions because Service is used to add
windows with multiple types.
This CL allows WindowProviderService to do so, but WindowProviderService
can only associate with the window type returned by #getWindowType.
This CL also extracts some methods to WindowContext interface so that
WindowContext and WindowProviderService can reuse the same interface.

Test: atest WindowContextPolicyTests StrictModeTest
Test: atest ContextIsUiContextTest ContextGetDisplayTest
Test: atest WindowContextTest WindowContextTests
fixes: 191959013

Change-Id: Ie16916b370a4cbb8a17ccaec9870d47b4b089390