Publish executables for pkldoc, pkl-codegen-java, pkl-codegen-kotlin (#1023)

This adds logic to build and publish the other executables related to Pkl.

These are:

* pkl-doc
* pkl-codegen-kotlin
* pkl-codegen-java

pkl-codegen-kotlin and pkl-codegen-java are published as executable JARs, whereas pkldoc is published both as an executable JAR, and also native executables (matching the set of os/arch supported by Pkl).

The reason this only publishes executable JARs for pkl-codegen-kotlin and pkl-codegen-java is because we expect that the Java requirement is not a problem for these users, and that the native executable provides negligible added value.

As part of this, the following changes are made:

* Introduce `pklJavaExecutable` plugin, which sets up building and publishing of executable JAR.
* Introduce `pklNativeExecutable` plugin, which sets up building and publishing of native executables.
* Introduce `NativeImageBuild` Gradle task, which knows how to build native-image executables.
* Introduce `ExecutableSpec` extension, for projects that publish executables to configure how those executables should be published.
* `./griddles buildNative`, by default, will only build the executable of the host OS/Arch, and will no longer cross-build.
* The target arch of `./gradlew buildNative` can be changed using `-Dpkl.targetArch=<aarch64|amd64>`.
* On linux/amd64 only, with `./gradlew buildNative`, a statically linked executable can be built using `-Dpkl.musl=true`
* Make `javaExecutable` a dependency of `assemble`
* Make `testStartJavaExecutable` a dependency of `check`
* Change name `pklNativeBuild` to `pklNativeLifecycle` to better match the plugin's purpose
* Remove Truffle SVM classes from main source set (don't publish these classes as part of the pkl-cli JAR)
* Change CircleCI definition to publish new executables
* Change CircleCI definition to call `buildNative` instead of individual task names

buildSrc/src/main/kotlin/ExecutableSpec.kt

@@ -0,0 +1,49 @@
+/*
+ * Copyright © 2025 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.
+ * You may obtain a copy of the License at
+ *
+ *     https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+import org.gradle.api.provider.Property
+
+abstract class ExecutableSpec {
+  /** The main entrypoint Java class of the executable. */
+  abstract val mainClass: Property<String>
+
+  /**
+   * The name of the native executable.
+   *
+   * Not required if not building a native executable.
+   */
+  abstract val name: Property<String>
+
+  /** The name of the Java executable. */
+  abstract val javaName: Property<String>
+
+  /** The name of the executable that shows in the description when published to Maven. */
+  abstract val documentationName: Property<String>
+
+  /**
+   * The base name of the Maven publication.
+   *
+   * This becomes the base name of the Artifact ID, with the os and arch suffixed.
+   *
+   * For example, `pkl` becomes `pkl-macos-aarch` for the macOS/aarch64 variant.
+   */
+  abstract val publicationName: Property<String>
+
+  /** The name of the artifact ID for the Java executable. */
+  abstract val javaPublicationName: Property<String>
+
+  /** The website for this executable. */
+  abstract val website: Property<String>
+}