Improve the jerry port api documents. #4288

Job	Run time
Clang_Unit_Build_Option_Tests	4m 21s
Checks	5m 30s
ASAN_Tests	3m 28s
ASAN_Tests_Debug	3m 47s
Conformance_Tests_ESNext	2m 8s
Conformance_Tests_ESNext_Debug_A	2m 9s
Conformance_Tests_ESNext_Debug_B	1m 18s
ESP_IDF_Build_Test	3m 37s
ESP8266_RTOS_SDK_Build_Test	1m 32s
Linux_AArch64_Tests	4m 22s
Linux_AArch64_Tests_Debug	8m 10s
Linux_ARMv7l_Tests	4m 24s
Linux_ARMv7l_Tests_Debug	6m 2s
Linux_x86_cpointer-32bit_Build_Correctness_Tests	1m 47s
Linux_x86-64_Build_Correctness_Debugger_Tests	5m 2s
Linux_x86-64_Build_Option_Tests	6m 45s
MbedOS_K64F_Build_Test	20m 47s
Notification	0s
NuttX_STM32F4_Build_Test	11m 3s
OSX_x86-64_Build_Correctness_Unit_Tests	4m 3s
OSX_x86-64_Build_Correctness_Unit_Tests_Debug	4m 58s
RIOT_STM32F4_Build_Test	1m 8s
UBSAN_Tests	2m 16s
Unit_Tests	1m 47s
Zephyr_STM32F4_Build_Test	3m 41s
	1h 54m 5s

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