feat(lsp): support Java class file contents and improve definition navigation handling

- Add `_lsp_java_class_file_contents` request to fetch contents of compiled Java classes via LSP (`java/classFileContents`).
- Handle `java/classFileContents` responses by opening a new buffer with Java syntax highlighting and inserting the returned source.
- Update definition handling to pass URI and range, enabling precise cursor placement after navigation.
- Detect `jdt://` URIs in `textDocument/definition` responses and request class file contents instead of direct navigation.
- Move goto navigation logic into `LSPServerEventsMixin`, using event system to access the active view and position the cursor.
- Expose `emit` and `emit_to` to the response cache for event dispatching.
- Restrict completion activation to `USER_REQUESTED`.
- Add TODO note about mapping language IDs to dedicated response handlers.

plugins/code/ui/lsp_manager/provider.py

@@ -60,9 +60,8 @@ class Provider(GObject.GObject, GtkSource.CompletionProvider):
     def do_get_activation(self):
         """ The context for when a provider will show results """
 #        return GtkSource.CompletionActivation.NONE
-#        return GtkSource.CompletionActivation.USER_REQUESTED
+        return GtkSource.CompletionActivation.USER_REQUESTED
 #        return GtkSource.CompletionActivation.INTERACTIVE
-        return GtkSource.CompletionActivation.INTERACTIVE | GtkSource.CompletionActivation.USER_REQUESTED
 
     def do_populate(self, context):
         results   = self.response_cache.filter_with_context(context)