Bug 1101461 - Use prototype-aware chai.assert.deepEqual to ease KB LayoutManager unit testing

- Also, modified user_press_manager_test that could potentially result in false negative (like bug 1101391)
Merge pull request #26935 from mnjul/bug_1101461_kb_test_cleanup

Bug 1101461 - Use prototype-aware chai.assert.deepEqual to ease KB LayoutManager unit testing. r=rudyl