Create soong-generated filesystem diff test

Running `m soong_generated_filesystem_tests` will diff the
soong-generated system image with the make-generated one.

Currently, this test fails, but we can start working on narrowing it
down now.

Bug: 371351099
Test: m soong_generated_filesystem_tests
Change-Id: I6e341607415b3676e758417a587f69c247652c3a