Make AssociationInfo immutable

This CL turns AssociationInfo into an immutable data class and
introduces a typesafe builder pattern for producing modified copies.

Note that this change now also invalidates the user cache entry when
making updates to associations.

Test: atest CtsCompanionDeviceManagerCoreTestCases
Test: atest CtsCompanionDeviceManagerUiAutomationTestCases
Change-Id: Ifd62d2ecce57790b6e462eb23033ca6c9a0cfe1b