Bump third_party/imgui/repo from `3c435c0` to `ee2119d` #5571

Job	Run time
Build on Linux (fake, gcc_release, clang, simulated)	53m 29s
Build on Linux (gcc_debug)	1h 5m 11s
Build on Darwin (clang, simulated)	36m 7s
Build on Linux (python_lib)	24m 54s
Build on Linux (coverage)	14m 16s
Build on Linux (python lighting-app)	5m 40s
	3h 19m 37s

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