Update Gradle to 8.11 (#800)

Changes:
- Update wrapper by running the following command:
  ./gradlew wrapper --gradle-version 8.11 --gradle-distribution-sha256-sum
  57dafb5c2622c6cc08b993c85b7c06956a2f53536432a30ead46166dbca0f1e9
- Verify wrapper JAR integrity according to:
  https://docs.gradle.org/current/userguide/gradle_wrapper.html#
  manually_verifying_the_gradle_wrapper_jar
- Replace usages of deprecated method `Project.exec` with `ExecOperations.exec`
- Convert extension function `Task.configureInstallGraalVm` to task class `InstallGraalVm`
  - a task class is the cleanest way to get hold of `ExecOperations`
- Move extension property `BuildInfo.GraalVm.downloadFile` into class `GraalVm`
- Don't apply plugin `pklGraalVm` in project `bench` (unnecessary, now causes error)

buildSrc/src/main/kotlin/BuildInfo.kt

@@ -50,6 +50,11 @@ open class BuildInfo(project: Project) {
       "https://download.oracle.com/graalvm/$jdkMajor/archive/$baseName.$extension"
     }
 
+    val downloadFile: File by lazy {
+      val extension = if (os.isWindows) "zip" else "tar.gz"
+      File(homeDir, "${baseName}.$extension")
+    }
+
     val installDir: File by lazy { File(homeDir, baseName) }
 
     val baseDir: String by lazy {