Add Count Class Instance API

This change introduces new APIs that allow developers to retrieve the
number of class instances, either by providing a single class or a list
of classes.

It also gives developers the option to exclude assignable types in the
counts that are returned.

Bug: 337354084
Test: atest CtsOsTestCases:DebugTest
Flag: android.os.count_class_instances_api
Change-Id: Iccb64190cddfffe23d7892ee76f175831061f7e3