Reduce number of copies of `stringEquals()` #744

Job	Run time
Lint	27s
GCC (5)	3m 37s
GCC (6)	3m 22s
GCC (7, -fsanitize=leak -fno-sanitize-recover=all)	3m 13s
GCC (8, -fsanitize=undefined -fno-sanitize-recover=all)	5m 11s
GCC (9, -fsanitize=address -fno-sanitize-recover=all)	5m 5s
GCC (10, -funsigned-char)	3m 39s
GCC (11)	3m 17s
Clang (3.8, -stdlib=libc++)	3m 17s
Clang (3.9, -stdlib=libc++)	3m 38s
Clang (4.0, -stdlib=libc++)	3m 29s
Clang (5.0)	3m 6s
Clang (6.0)	4m 29s
Clang (7)	3m 38s
Clang (8, -fsanitize=leak -fno-sanitize-recover=all)	3m 18s
Clang (9, -fsanitize=undefined -fno-sanitize-recover=all)	3m 49s
Clang (10, -fsanitize=address -fno-sanitize-recover=all)	3m 37s
XCode (11.7)	4m 24s
XCode (12.4)	4m 41s
XCode (13.2.1)	6m 59s
Clang-Tidy	5m 0s
Arduino (arduino:avr, arduino:avr:uno)	39s
Arduino (arduino:samd, arduino:samd:mkr1000)	1m 12s
Test configuration on Windows	55s
Test configuration on Linux	46s
PlatformIO (atmelavr, leonardo, SD, Ethernet, avr)	40s
PlatformIO (espressif8266, huzzah, esp8266)	3m 40s
PlatformIO (espressif32, esp32dev, Ethernet, esp8266)	2m 10s
PlatformIO (atmelsam, mkr1000USB, SD, Ethernet, esp8266)	1m 0s
PlatformIO (teensy, teensy31, esp8266)	1m 29s
PlatformIO (ststm32, adafruit_feather_f405, SD, Ethernet, esp8266)	2m 33s
PlatformIO (nordicnrf52, adafruit_feather_nrf52840, SD, Ethernet, esp8266)	2m 26s
GCC for ARM processor	3m 48s
Coverage	3m 3s
Particle (argon)	29s
Valgrind	2m 32s
Amalgamate ArduinoJson.hpp	6s
Amalgamate ArduinoJson.h	7s
CodeQL	13m 47s
ESP-IDF	2m 27s
	2h 5m 5s

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