Switch to JDK 18 as minumum supported version

[deejay1]

Switches to 18 as base release having the minimum supported features. Adds matrix build for JDK versions up to 21.

[piotrrzysko]

Thanks for the PR.

I'm fine with adding Java 21 to the CI, but unless there's a reason to drop support for earlier versions, I'd prefer not to do so. Some users would like to even support Java 17, as mentioned in issue #28.

My suggestion would be to create a separate GitHub job that utilizes Java 21 for building and testing the library. We can set this up using a matrix.

[deejay1]

Thanks for the PR.

I'm fine with adding Java 21 to the CI, but unless there's a reason to drop support for earlier versions, I'd prefer not to do so. Some users would like to even support Java 17, as mentioned in issue #28.

My suggestion would be to create a separate GitHub job that utilizes Java 21 for building and testing the library. We can set this up using a matrix.

Switched to a matrix build and to 18 as the minimal version with all required features that are used now.

[piotrrzysko]

In the README there are two places where the required Java version is mentioned:

• https://github.com/simdjson/simdjson-java/blob/main/README.md?plain=1#L50
• https://github.com/simdjson/simdjson-java/blob/main/README.md?plain=1#L90

If we want to start supporting Java 18, we need to update the README.

[piotrrzysko]

Looks good. Thanks again!