Cosindering using Gradle Java toolchain to avoid Java 11 check

When you add gradle Java toolchain to this project it literally doesn't matter which jvm version users (potential contributors) are using to build the project. As long as it can run gradle, the toolchain will make sure that the correct jvm version will be downloaded and used to build the project.

See https://docs.gradle.org/current/userguide/toolchains.html

There is no need for the "is Java 11 check" in the settings.gradle anymore. Additionally, also CI would use that exact same jdk version.

Idea is coming from https://github.com/apple/pkl/issues/181

Start in settings.gradle by reading the existing Java 11 check, then consult the Gradle Java toolchains documentation linked in the issue. Inspect the project's CI configuration to determine how the JDK is selected. Done means the check is no longer needed and local builds and CI use the same toolchain version.

Written by the indexing model from the issue text.