Add jerry-ext amalgamation #4284

Job	Run time
ASAN_Tests	3m 53s
ASAN_Tests_Debug	3m 27s
Clang_Unit_Build_Option_Tests	4m 6s
Checks	5m 21s
Conformance_Tests_ESNext	2m 8s
Conformance_Tests_ESNext_Debug_A	2m 7s
Conformance_Tests_ESNext_Debug_B	1m 17s
ESP_IDF_Build_Test	3m 37s
ESP8266_RTOS_SDK_Build_Test	1m 27s
Linux_AArch64_Tests	4m 22s
Linux_AArch64_Tests_Debug	6m 40s
Linux_ARMv7l_Tests	4m 22s
Linux_ARMv7l_Tests_Debug	5m 57s
Linux_x86_cpointer-32bit_Build_Correctness_Tests	1m 45s
Linux_x86-64_Build_Correctness_Debugger_Tests	5m 5s
Linux_x86-64_Build_Option_Tests	4m 19s
MbedOS_K64F_Build_Test	1m 25s
Notification	0s
NuttX_STM32F4_Build_Test	2m 21s
OSX_x86-64_Build_Correctness_Unit_Tests	3m 22s
OSX_x86-64_Build_Correctness_Unit_Tests_Debug	5m 18s
RIOT_STM32F4_Build_Test	1m 5s
UBSAN_Tests	2m 10s
Unit_Tests	1m 48s
Zephyr_STM32F4_Build_Test	3m 2s
	1h 20m 24s

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