ENH allow stacked messages on FormMessage #1676

Job	Run time
CI / Generate matrix	9s
CI / Context	1s
CI / Check governance	4s
CI / 8.1 prf-low mysql57 phpunit framework-core	4m 52s
CI / 8.1 mysql57 phpunit framework-core	6m 45s
CI / 8.2 mysql80 phpunit framework-core	8m 44s
CI / 8.1 prf-low mysql57 phpunit framework-orm	14m 18s
CI / 8.1 mysql57 phpunit framework-orm	11m 15s
CI / 8.2 mysql80 phpunit framework-orm	18m 16s
CI / 8.1 prf-low mysql57 phpunit cms	1m 56s
CI / 8.1 mysql57 phpunit cms	1m 43s
CI / 8.2 mysql80 phpunit cms	2m 28s
CI / 8.1 mysql57 phplinting	1m 40s
CI / Check unreleased changes	0s
CI / Patch release	0s
	1h 12m 11s

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