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-core/pkl-core.gradle.kts

@@ -98,20 +98,22 @@ tasks.processResources {
   inputs.property("version", buildInfo.pklVersion)
   inputs.property("commitId", buildInfo.commitId)
 
-  filesMatching("org/pkl/core/Release.properties") {
-    val stdlibModules =
-      fileTree("$rootDir/stdlib") {
-          include("*.pkl")
-          exclude("doc-package-info.pkl")
-        }
-        .map { "pkl:" + it.nameWithoutExtension }
-        .sortedBy { it.lowercase() }
+  val pklVersion = buildInfo.pklVersion
+  val commitId = buildInfo.commitId
+  val stdlibModules =
+    fileTree("$rootDir/stdlib") {
+        include("*.pkl")
+        exclude("doc-package-info.pkl")
+      }
+      .map { "pkl:" + it.nameWithoutExtension }
+      .sortedBy { it.lowercase() }
 
+  filesMatching("org/pkl/core/Release.properties") {
     filter<ReplaceTokens>(
       "tokens" to
         mapOf(
-          "version" to buildInfo.pklVersion,
-          "commitId" to buildInfo.commitId,
+          "version" to pklVersion.get(),
+          "commitId" to commitId.get(),
           "stdlibModules" to stdlibModules.joinToString(","),
         )
     )
@@ -140,13 +142,15 @@ val externalReaderFixture by tasks.registering {
   group = "build"
   dependsOn(tasks.named("compileExternalReaderFixtureJava"))
   inputs.files(externalReaderFixtureSourceSet.map { it.output })
-  val fileName = if (buildInfo.os.isWindows) "externalreader.bat" else "externalreader"
+  val isWindows = buildInfo.os.isWindows
+  val fileName = if (isWindows) "externalreader.bat" else "externalreader"
   val outputFile = layout.buildDirectory.file("fixtures/$fileName")
   outputs.file(outputFile)
+  val runtimeClasspath = externalReaderFixtureSourceSet.map { it.runtimeClasspath }
   doLast {
-    val classpath = externalReaderFixtureSourceSet.get().runtimeClasspath.asPath
+    val classpath = runtimeClasspath.get().asPath
     val scriptContent =
-      if (buildInfo.os.isWindows) {
+      if (isWindows) {
         """
           @echo off
           java -cp $classpath org.pkl.core.externalreaderfixture.Main