zlib sample build fixes for Gradle 8 or later

[atsushieno]

context: #33 (comment)

There is no reason I do not contribute these local changes back ;-)

[saudet]

So, upgrading to Gradle 8.x forces us to write more code for the build files? But you said that Gradle 8.x actually makes it possible to write less code... Personally, I've given up on Gradle. They change everything on every minor release, but it still never quite does what it's actually supposed to do. If @HGuillemet says there's no better way to get Gradle 8.x working, I'll merge this though. Thanks for the contribution!

[atsushieno]

I didn't analyze Gradle 7 behavior in particular. It's going to be refused by any newer versions of IDEA platforms (minimum supported Gradle version).

If anyone intends to use specific Gradle version, gradle directory and Gradle wrapper files need to be checked in to the repo. That's what people do in Android and Kotlin ecosystem.

(I understand your pain and I want to dump Gradle and switch to mvn directly too, but we are consuming it in Kotlin ecosystem where only Gradle is used. So if gradle-javacpp does not work there, then we will have to give up entire JavaCPP.)