Add tests for the new logic in ime_processing.js, which extracts
properties from WindowManager and SurfaceFlinger trace entries and
combines them into IME trace entries.
Some simple IME, WM and SF traces are added into
spec/traces/ime_processing_traces, and the results of combining them are
asserted for in spec/ImeProcessingSpec.js.
Bug: 237744706
Test: yarn run test
Change-Id: If2a053c4885cc4c522c93cf747b94cb69aceb1c6