Add test to IME local insets handling

Add test to make sure the traversal of insets update doesn't
accidentally adding local insets to IME from the target window.

Test: WindowStateTests
Test: The test will fail without the change of 46ca92cc
Bug: 421000153
Bug: 441434842
Flag: EXEMPT TEST_ONLY
Change-Id: I7efe7a0a12a1e666f31e7bda7afd1c6852459ae6