Enable Gradle configuration cache (#1646)

Enable the configuration cache feature in Gradle, and adjust various
pieces of build logic that aren't configuration cache compatible.

pkl-tools/pkl-tools.gradle.kts

@@ -81,13 +81,14 @@ private fun Exec.configureTestStartFatJar(launcher: Provider<JavaLauncher>) {
 
   inputs.files(tasks.shadowJar)
   executable = launcher.get().executablePath.asFile.absolutePath
-  standardOutput = OutputStream.nullOutputStream()
+  doFirst { standardOutput = OutputStream.nullOutputStream() }
 
+  val shadowJarFile = tasks.shadowJar.flatMap { it.archiveFile }
   argumentProviders.add(
     CommandLineArgumentProvider {
       buildList {
         add("-cp")
-        add(tasks.shadowJar.get().outputs.files.singleFile.absolutePath)
+        add(shadowJarFile.get().asFile.absolutePath)
         add("org.pkl.cli.Main")
         add("eval")
         add("-x")
@@ -163,7 +164,7 @@ publishing {
           connection.set("scm:git:git://github.com/apple/pkl.git")
           developerConnection.set("scm:git:ssh://github.com/apple/pkl.git")
           val buildInfo = project.extensions.getByType<BuildInfo>()
-          url.set("https://github.com/apple/pkl/tree/${buildInfo.commitish}")
+          url.set(buildInfo.commitish.map { "https://github.com/apple/pkl/tree/$it" })
         }
         issueManagement {
           system.set("GitHub Issues")