Adding Api that allows apps to provide URI to be utilized to switch user's...

Adding Api that allows apps to provide URI to be utilized to switch user's session to another surface

Adds EXTRA_SESSION_TRANSFER_WEB_URI to AssistContent which allows an application to provide a URI with information that will assist in switching the user's session to another surface. The "Open in browser" feature will use this URI to transition the current session from one surface to the other.  Apps may choose to encode session or user information into this URI in order to provide a better session transfer experience.

Design Doc: go/app-to-web-api
Bug: 373680430
Flag:com.android.window.flags.enable_desktop_windowing_app_to_web_education
Test: m

Change-Id: I103181ed475b08f46c3a4c55fb692beb678b56a2