Bump third_party/imgui/repo from `3c435c0` to `1d96282` #6062

Job	Run time
REPL Tests - Linux	1h 35m 59s
Test Suites - Darwin (no-ble-no-shell-asan-clang)	1h 18m 21s
Test Suites - Linux (no-ble-no-shell-tsan-clang)	2h 1m 24s
Test Suites - Darwin (no-ble-no-shell-tsan-clang)	1h 51m 19s
REPL Tests - Darwin	0s
	6h 47m 3s

Provide feedback