Apply trailer only optimization for responseForSingleElement #1008

Job	Run time
Checks	2m 7s
Compile Benchmarks	1m 26s
Compile and test (2.12.20, 8)	3m 50s
Gradle tests	3m 31s
Compile and test (2.12.20, 11)	4m 18s
Maven tests	2m 28s
Compile and test (2.12.20, 17)	4m 3s
sbt scripted tests (gen-scala-server, 2.12)	8m 12s
Compile and test (2.12.20, 21)	3m 43s
sbt scripted tests (gen-java, 2.12)	3m 41s
Docs	3m 34s
Compile and test (2.13.15, 8)	4m 38s
Compile and test (2.13.15, 11)	4m 28s
Compile and test (2.13.15, 17)	4m 36s
Compile and test (2.13.15, 21)	4m 17s
Compile and test (3.3.4, 8)	4m 31s
Compile and test (3.3.4, 11)	4m 37s
Compile and test (3.3.4, 17)	4m 44s
Compile and test (3.3.4, 21)	4m 5s
	1h 16m 49s

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