Ensure array_type has front() method + fix array_type on jsoncpp #583

Job	Run time
custom-install-linux	10s
custom-install-win	2m 55s
default-linux	9s
default-linux-with-examples	6s
default-win	3m 9s
min-req	6m 15s
preset-support-but-not-enough	8m 26s
root-hint-install-linux	8s
no-base64	11s
no-pico	15s
with-hunter	2m 40s
with-libressl	2m 15s
with-wolfssl	1m 10s
	27m 49s

Provide feedback