chore: move the JDT LS components out of plugins/ (#1292)

java-usages, kotlin-bridge and the patched Lombok agent are JDT LS bundles and a Java agent embedded into the app, not OpenIDEA plugins. Move them to java/ so plugins/ holds only plugins, and update the paths that embed or mention them.

Also fix the stale build path in the hello fixture and the contributor guide's layout (there is no templates/ directory; starter templates live in the openidea-plugin CLI).

java/java-usages/MANIFEST.MF

@@ -0,0 +1,11 @@
+Manifest-Version: 1.0
+Bundle-ManifestVersion: 2
+Bundle-Name: OpenIDEA Java usages
+Bundle-SymbolicName: ai.openidea.usages;singleton:=true
+Bundle-Version: 1.3.0
+Bundle-RequiredExecutionEnvironment: JavaSE-21
+Require-Bundle: org.eclipse.jdt.ls.core,org.eclipse.jdt.core,
+ org.eclipse.jdt.core.manipulation,org.eclipse.core.runtime,
+ org.eclipse.lsp4j,org.eclipse.core.resources,com.google.gson,
+ org.eclipse.ltk.core.refactoring
+