feat: add getImportClassContent method to collect import class info

Author: wenytang-ms

jdtls.ext/com.microsoft.jdtls.ext.core/plugin.xml

@@ -10,6 +10,7 @@
             <command id="java.project.getMainClasses" />
             <command id="java.project.generateJar" />
             <command id="java.project.checkImportStatus" />
+            <command id="java.project.getImportClassContent" />
         </delegateCommandHandler>
     </extension>
     <extension

jdtls.ext/com.microsoft.jdtls.ext.core/src/com/microsoft/jdtls/ext/core/CommandHandler.java

@@ -37,6 +37,8 @@ public Object executeCommand(String commandId, List<Object> arguments, IProgress
                     return ProjectCommand.exportJar(arguments, monitor);
                 case "java.project.checkImportStatus":
                     return ProjectCommand.checkImportStatus();
+                case "java.project.getImportClassContent":
+                    return ProjectCommand.getImportClassContent(arguments, monitor);
                 default:
                     break;
             }