## Context

JEI needs client tests that can start external dedicated servers.

Today, doing that from another project means reading MDG generated classpath, VM args, and program args files directly. That works, but it depends on internal `build/moddev` file names and requires downstream code to know how MDG assembles a launch command.

## Changes

This change adds a public `CreateLaunchMetadata` task for each configured run.

For a run named `server`, MDG registers:

```groovy
createServerLaunchMetadata
```

The task writes:

```text
build/moddev/serverLaunchMetadata.properties
```

The properties file contains:

- `workingDirectory`
- `javaExecutable`
- `classpathArgsFile`
- `vmArgsFile`
- `programArgsFile`
- `mainClass`
- `modFolders`
- `environment.<name>` entries for run environment variables

There is also a `createLaunchMetadata` aggregate task.

The metadata writer uses the JDK Properties format so consumers can load it with standard properties readers, while MDG keeps the output sorted and comment-free for stable task output.

Launchers should treat `workingDirectory` as part of the metadata contract. If they need disposable or test-specific state, they should configure the run `gameDirectory` instead of replacing the metadata working directory at launch time.

This also adds Gradle daemon JVM criteria for Java 17 so local wrapper invocations use a supported JVM by default.

## Why

This gives consumers like JEI a typed Gradle task output to depend on:

```groovy
tasks.named("createServerLaunchMetadata", CreateLaunchMetadata).flatMap {
    it.metadataFile
}
```

Downstream builds can use the metadata without reconstructing MDG launch details from internal file naming conventions.

## Validation

- `./gradlew test --tests net.neoforged.moddevgradle.tasks.CreateLaunchMetadataTest`
- `./gradlew test --tests net.neoforged.moddevgradle.functional.LaunchMetadataFunctionalTest`
- `./gradlew javaImmaculateCheck`

JEI validated this branch with `--include-build ../ModDevGradle`:

- `:NeoForge:runClientRecipeSyncTest`
- NeoForge external server with JEI passed
- NeoForge external server without JEI passed
- vanilla external server without JEI passed

JEI configures each external server run with a JEI-owned build directory as `gameDirectory`, consumes `CreateLaunchMetadata`, and launches using the metadata `workingDirectory` unchanged.

Coverage includes:

- per-run metadata
- the `createLaunchMetadata` aggregate task
- generated arg-file paths
- properties escaping and ordering