Apply trailer only optimization for responseForSingleElement (#396) #1009

Job	Run time
Docs	3m 17s
Checks	2m 0s
Compile Benchmarks	1m 27s
Compile and test (2.12.20, 8)	4m 0s
Compile and test (2.12.20, 11)	4m 11s
Gradle tests	3m 8s
sbt scripted tests (gen-scala-server, 2.12)	8m 5s
Compile and test (2.12.20, 17)	3m 47s
Maven tests	2m 37s
sbt scripted tests (gen-java, 2.12)	3m 41s
Compile and test (2.12.20, 21)	3m 42s
Compile and test (2.13.15, 8)	4m 28s
Compile and test (2.13.15, 11)	4m 12s
Compile and test (2.13.15, 17)	4m 32s
Compile and test (2.13.15, 21)	3m 47s
Compile and test (3.3.4, 8)	4m 44s
Compile and test (3.3.4, 11)	4m 51s
Compile and test (3.3.4, 17)	4m 22s
Compile and test (3.3.4, 21)	4m 12s
	1h 15m 3s

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