Tests

Bump third_party/imgui/repo from `88fec09` to `46843b6` #1418

Job	Run time
REPL Tests - Linux	29m 5s
Test Suites - Darwin (no-ble-asan-clang)	1h 23m 0s
Test Suites - Darwin (no-ble-tsan-clang)	2h 12m 3s
Test Suites - Linux (no-ble-tsan-clang)	1h 35m 59s
REPL Tests - Darwin	0s
	5h 40m 7s

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