Introduce UserData and UserDataRepository

UserData is designed to hold all the IMMS per-user data.
This CL just introduces the class, data will be moved in the next CLs.

This is a refactoring CL only and no regression should be expected.

Bug: 325515685
Test: atest FrameworksInputMethodSystemServerTests
Test: atest CtsInputMethodTestCases
Test: atest FrameworksServicesTests
Test: atest --host FrameworksInputMethodSystemServerTestsRavenwood
Change-Id: I20ac0c613fed98afc1c2c0fadd6ac80403b7babf