Remove Gradle Wrapper version output from user manual (#9000)* Remove Gradle Wrapper version output from user manualIt would take far too much effort to ensure that the sample in the GradleWrapper reference chapter that shows the output of running `./gradlew -v`is consistent with the current version of Gradle. Since it doesn't providea lot of value to the reader, I've just removed it.
Externalize samples testing infrastructureThis change replaces UserGuideSamplesRunner with an external librarycalled sample-check. Sample discovery, execution, and normalizationis delegated to this library, with some custom normalizers remainingin the Gradle codebase.Samples output has become co-located with the sample code. Samples testsmust be run with Java 8+.