Support Gradle toolchains

[mleegwt]

Since Gradle 7 toolchains are supported by Gradle. See https://docs.gradle.org/current/userguide/toolchains.html
It would be awesome to support them that way instead of the 'magic' lookup that is currently implemented.

[Horcrux7]

Why you can't use it? I am not familiar with this new API. But I think the follow snipped should work:

setupBuilder {
    def javaLauncher = javaToolchains.launcherFor {
        languageVersion = JavaLanguageVersion.of(14)
    }
    bundleJre = javaLauncher.metadata.installationPath
}

If this not work you can try javaLauncher.metadata.installationPath.asFile.absolutePath.