[52/n] LetterboxTaskInfoRepository implementation

Creates LetterboxTaskInfoRepository as the
MemoryRepositoryImplementation to store TaskInfo
data for a given Task using the taskId as key.

This is useful to use some TaskInfo properties when
the TaskInfo object is not present in Change.

Flag: com.android.window.flags.app_compat_refactoring
Bug: 309593314
Test: atest WMShellUnitTests:MemoryRepositoryImplTest

Change-Id: Iae5d453ef8400e5d1d0d8d799824835a7eb8ea57