Implement optional chaining #4194

Job	Run time
Checks	5m 27s
ASAN_Tests_Debug	3m 50s
ASAN_Tests	3m 41s
Clang_Unit_Build_Option_Tests	4m 17s
Conformance_Tests_ESNext	2m 16s
Conformance_Tests_ESNext_Debug_A	2m 9s
Conformance_Tests_ESNext_Debug_B	1m 22s
ESP_IDF_Build_Test	3m 49s
ESP8266_RTOS_SDK_Build_Test	1m 29s
Linux_AArch64_Tests	4m 22s
Linux_AArch64_Tests_Debug	7m 3s
Linux_ARMv7l_Tests	4m 22s
Linux_ARMv7l_Tests_Debug	5m 47s
Linux_x86_cpointer-32bit_Build_Correctness_Tests	1m 44s
Linux_x86-64_Build_Correctness_Debugger_Tests	4m 58s
Linux_x86-64_Build_Option_Tests	4m 27s
MbedOS_K64F_Build_Test	1m 35s
Notification	0s
NuttX_STM32F4_Build_Test	2m 8s
OSX_x86-64_Build_Correctness_Unit_Tests	3m 5s
OSX_x86-64_Build_Correctness_Unit_Tests_Debug	3m 51s
RIOT_STM32F4_Build_Test	1m 9s
UBSAN_Tests	2m 9s
Unit_Tests	1m 52s
Zephyr_STM32F4_Build_Test	3m 22s
	1h 20m 14s

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