fix: treat 'void' qualified name as VoidType in Java action return type

'returns void' parses as a bare qualified name (TypeEnumeration with
EnumRef{Name:"void"}) because the grammar has no VOID keyword in the
dataType rule. astDataTypeToJavaActionReturnType was falling through to
the EntityType case, producing EntityType{Entity:".void"}, which caused
CE1613 "The selected entity '.void' no longer exists." in Studio Pro.

Fix: when the resolved entity name is "void" (case-insensitive, with or
without the empty-module dot prefix), return VoidType instead.

Also restore the full empty_java_action_argument.mdl content (module,
entity, and java action setup) that was dropped during the rebase of the
misc branch — git skipped the upstream fixup commits that added them.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: ako

mdl/executor/cmd_javaactions.go

@@ -571,12 +571,21 @@ func astDataTypeToJavaActionReturnType(dt ast.DataType) javaactions.CodeActionRe
 	case ast.TypeEntity, ast.TypeEnumeration:
 		// TypeEnumeration with a qualified name is treated as entity type here,
 		// since the visitor can't distinguish entity types from enumeration types.
+		// "void" parses as a bare qualified name; treat it as VoidType.
 		entityName := ""
 		if dt.EntityRef != nil {
 			entityName = dt.EntityRef.Module + "." + dt.EntityRef.Name
 		} else if dt.EnumRef != nil {
 			entityName = dt.EnumRef.Module + "." + dt.EnumRef.Name
 		}
+		if strings.EqualFold(strings.TrimPrefix(entityName, "."), "void") {
+			return &javaactions.VoidType{
+				BaseElement: model.BaseElement{
+					ID:       model.ID(types.GenerateID()),
+					TypeName: "CodeActions$VoidType",
+				},
+			}
+		}
 		return &javaactions.EntityType{
 			BaseElement: model.BaseElement{
 				ID:       model.ID(types.GenerateID()),