fix(java): run the language server on a JDK so the debugger can start (#815)

The managed runtime for the Java language server was a Temurin JRE, which lacks jdk.jdi. java-debug runs inside the jdtls JVM, so Debug failed with NoClassDefFoundError com/sun/jdi/VMDisconnectedException and "debug adapter did not answer initialize in time" while Run worked. Provision a full JDK instead and replace an already-downloaded JRE runtime (Temurin's JRE lists jdk.jdi in release MODULES although the image omits it, so suitability checks IMAGE_TYPE, javac and the modules); auto-picked installed runtimes must also carry jdk.compiler, jdk.jdi and jdk.unsupported, and a user-chosen language-server JDK without them gets a clear warning. Fixes #765.

crates/ide-core/src/java_runtime.rs

@@ -0,0 +1,25 @@
+//! Capabilities needed by the JVM hosting Java language-server bundles.
+
+use std::path::Path;
+
+/// jdtls' javac bundle, java-debug / hot code replace, and Lombok / Gradle tooling.
+const BUNDLE_MODULES: &[&str] = &["jdk.compiler", "jdk.jdi", "jdk.unsupported"];
+
+/// Require a full JDK, including the modules used by jdtls and its bundles.
+/// Temurin JREs can list the build JDK's modules in `release` even when the runtime
+/// image omits them, so module metadata alone does not establish suitability.
+pub fn supports_java_bundles(home: &Path) -> bool {
+    let Ok(release) = std::fs::read_to_string(home.join("release")) else { return false };
+    let property =
+        |key: &str| release.lines().find_map(|line| line.trim().strip_prefix(key)).map(|v| v.trim().trim_matches('"'));
+    let javac = if cfg!(windows) { "javac.exe" } else { "javac" };
+    if property("IMAGE_TYPE=").is_some_and(|image| image.eq_ignore_ascii_case("jre"))
+        || !home.join("bin").join(javac).is_file()
+    {
+        return false;
+    }
+    match property("MODULES=") {
+        Some(modules) => BUNDLE_MODULES.iter().all(|required| modules.split_whitespace().any(|m| m == *required)),
+        None => BUNDLE_MODULES.iter().all(|m| home.join("jmods").join(format!("{m}.jmod")).is_file()),
+    }
+}