Upgrade JVM toolchain to 25 and Kotlin toolchain to 2.3.20 (#1516)

Motivation
- Enable correct NullAway analysis
- Pick up toolchain fixes and improvements

Toolchains
- Require JDK 25 for JVM toolchain (keep Java 17 runtime compatibility)
- Require Kotlin 2.3.20 for Kotlin toolchain (keep Kotlin 2.2 runtime
compatibility)
- Require JDK 25 for Gradle daemon JVM (via
gradle-daemon-jvm.properties)
- Fix javac and kotlinc warnings from toolchain upgrades

CI
- Bump GitHub workflows to JDK 25

Building Kotlin
- Bump Kotlin language level to 2.2 to match stdlib version
- Consolidate build logic into pklKotlinBase.gradle.kts
- Adopt modern Kotlin plugin syntax
- Fix new kotlinc warnings
- Update ktfmt to 0.62
  - first version compatible with Kotlin 2.3.20
  - changes formatting compared to 0.61
- Replace dependency resolution rule with BOM alignment
  - rule was too broad and interfered with toolchain/runtime separation

Testing
- Expand matrix to JDK 25 (LTS) and 26
- Ensure each matrix task can be run independently
- Fix KotlinCodeGeneratorsTest and EmbeddedExecutorsTest on affected
JDKs
- Disable one test in CliCommandTest on affected JDKs (failure cause
unknown)

Compatibility fixes
- Fix reflective access in DocGenerator on affected JDKs

Build fixes
- Fix misuse of `task.enabled` vs. `report.required`
- Fix `gradlew tasks` on Windows
- Downgrade Spotless to 8.3.0 to (hopefully) work around sporadic
NoClassDefFoundError

Result
- NullAway runs correctly
- Broader JDK test coverage
- More reproducible and potentially faster builds

pkl-executor/pkl-executor.gradle.kts

@@ -1,5 +1,5 @@
 /*
- * Copyright © 2024-2025 Apple Inc. and the Pkl project authors. All rights reserved.
+ * Copyright © 2024-2026 Apple Inc. and the Pkl project authors. All rights reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -20,7 +20,6 @@ plugins {
   pklAllProjects
   pklJavaLibrary
   pklPublishLibrary
-  pklKotlinTest
 }
 
 val pklDistributionCurrent: Configuration by configurations.creating
@@ -55,7 +54,7 @@ publishing {
         description.set(
           """
           Library for executing Pkl code in a sandboxed environment.
-        """
+          """
             .trimIndent()
         )
       }
@@ -65,37 +64,37 @@ publishing {
 
 sourceSets { main { java { srcDir("src/main/java") } } }
 
-val prepareHistoricalDistributions by
-  tasks.registering {
-    val outputDir = layout.buildDirectory.dir("pklHistoricalDistributions")
-    inputs.files(pklHistoricalDistributions.files)
-    outputs.dir(outputDir)
-    doLast {
-      val distributionDir = outputDir.get().asFile.toPath().also(Files::createDirectories)
-      for (file in pklHistoricalDistributions.files) {
-        val target = distributionDir.resolve(file.name)
-        // Create normal files on Windows, symlink on macOS/linux (need admin privileges to create
-        // symlinks on Windows)
-        if (buildInfo.os.isWindows) {
-          if (!Files.isRegularFile(target, LinkOption.NOFOLLOW_LINKS)) {
-            if (Files.exists(target)) {
-              Files.delete(target)
-            }
-            Files.copy(file.toPath(), target)
+val prepareHistoricalDistributions by tasks.registering {
+  val outputDir = layout.buildDirectory.dir("pklHistoricalDistributions")
+  inputs.files(pklHistoricalDistributions.files)
+  outputs.dir(outputDir)
+  doLast {
+    val distributionDir = outputDir.get().asFile.toPath().also(Files::createDirectories)
+    for (file in pklHistoricalDistributions.files) {
+      val target = distributionDir.resolve(file.name)
+      // Create normal files on Windows, symlink on macOS/linux (need admin privileges to create
+      // symlinks on Windows)
+      if (buildInfo.os.isWindows) {
+        if (!Files.isRegularFile(target, LinkOption.NOFOLLOW_LINKS)) {
+          if (Files.exists(target)) {
+            Files.delete(target)
           }
-        } else {
-          if (!Files.isSymbolicLink(target)) {
-            if (Files.exists(target)) {
-              Files.delete(target)
-            }
-            Files.createSymbolicLink(target, file.toPath())
+          Files.copy(file.toPath(), target)
+        }
+      } else {
+        if (!Files.isSymbolicLink(target)) {
+          if (Files.exists(target)) {
+            Files.delete(target)
           }
+          Files.createSymbolicLink(target, file.toPath())
         }
       }
     }
   }
+}
 
-val prepareTest by
-  tasks.registering { dependsOn(pklDistributionCurrent, prepareHistoricalDistributions) }
+val prepareTest by tasks.registering {
+  dependsOn(pklDistributionCurrent, prepareHistoricalDistributions)
+}
 
 tasks.test { dependsOn(prepareTest) }