Move WindowContext module to window package

In this way, we can clarify the owners and it is easier to maintain.
Also refactor to move WindowContext creation logic to ContextImpl.

Test: atest WindowContext WindowContextTests WindowContextPolicyTests
Bug: 159767464
Bug: 152193787

Change-Id: I78432aa18aa97e001f5a9a04321109e456fd137b
17 files changed