Tests

Bump third_party/imgui/repo from `3816d47` to `313676d` #5273

Job	Run time
Test Suites - Linux (no-ble-tsan-clang)	1h 30m 49s
REPL Tests - Linux	36m 20s
Test Suites - Darwin (no-ble-asan-clang)	1h 35m 20s
Test Suites - Darwin (no-ble-tsan-clang)	1h 38m 7s
REPL Tests - Darwin	0s
	5h 20m 36s

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