Fix #301: WhenAll wait-all + aggregate-exception semantics (root cause of rewind deadlock) #326

Job	Run time
build (22.x)	26s
discover	4s
samples-with-emulator (unit-testing, 22.x)	23s
samples-with-emulator (basics, 22.x)	34s
samples-with-emulator (versioning, 22.x)	34s
samples-with-emulator (lifecycle-management, 22.x)	28s
samples-with-emulator (retry-and-error-handling, 22.x)	33s
samples-with-emulator (human-interaction, 22.x)	38s
samples-with-emulator (query-and-history, 22.x)	27s
samples-with-emulator (hello-orchestrations, 22.x)	33s
samples-no-emulator	0s
samples-gate	3s
	4m 43s

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