Bump third_party/imgui/repo from `001f102` to `454f36d` #1103

Job	Run time
REPL Tests - Linux	27m 24s
Test Suites - Darwin (no-ble-asan-clang)	1h 20m 6s
Test Suites - Darwin (no-ble-tsan-clang)	1h 37m 39s
Test Suites - Linux (no-ble-tsan-clang)	1h 37m 33s
REPL Tests - Darwin	0s
	5h 2m 42s

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