Add missing JavaScript in-depth.html documentation #842

Job	Run time
Test Browser on macOS (safari, main)	1m 8s
Test Build	25s
Test Browser on macOS (safari, disabled)	1m 24s
Test Shell (jsc, main)	51s
Test Browser on Linux (chrome, main)	37s
Test Shell (v8, default)	2m 45s
Test Browser on Linux (chrome, default)	1m 22s
Test Shell (jsc, default)	3m 20s
Test Shell (v8, main)	41s
Test Shell (spidermonkey, default)	5m 34s
Test Shell (jsc, disabled)	1m 48s
Test Shell (spidermonkey, disabled)	1m 55s
Test Shell (spidermonkey, main)	46s
Test Shell (v8, disabled)	1m 36s
Test Browser on Linux (firefox, default)	1m 44s
Test Browser on macOS (safari, default)	1m 58s
Test Browser on Linux (firefox, disabled)	1m 27s
Test Browser on Linux (chrome, disabled)	1m 1s
Test Browser on Linux (firefox, main)	43s
	31m 5s

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