Bump third_party/imgui/repo from `03298fe` to `7f9533b` #348

Job	Run time
REPL Tests - Darwin	0s
REPL Tests - Linux	33m 55s
Test Suites - Darwin (no-ble-asan-clang)	1h 16m 15s
Test Suites - Darwin (no-ble-tsan-clang)	1h 46m 8s
Test Suites - Linux (no-ble-tsan-clang)	1h 43m 3s
	5h 19m 21s

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