[refact](inverted index) refact compound idx writer (apache#59219)

### What problem does this PR solve?
This PR refactors the compound index writer for the inverted index V2
format to optimize performance, particularly for cloud storage systems
like S3. The main improvement is bypassing unnecessary directory
operations by directly creating the output stream using an existing file
writer.

Key changes:

Added a static factory method FSIndexOutputV2::create() for direct
instantiation without requiring a Directory object
Refactored IndexStorageFormatV2::create_output_stream() to return only
an IndexOutput instead of a Directory-IndexOutput pair
Removed the cloud mode check in DorisFSDirectoryFactory::getDirectory()
to simplify code (directory creation is safe for all file systems)

Author: airborne12

be/src/olap/rowset/segment_v2/inverted_index_fs_directory.cpp

@@ -925,28 +925,25 @@ DorisFSDirectory* DorisFSDirectoryFactory::getDirectory(const io::FileSystemSPtr
     if (config::inverted_index_ram_dir_enable && can_use_ram_dir) {
         dir = _CLNEW DorisRAMFSDirectory();
     } else {
-        // cloud mode does not need to create directory
-        if (!config::is_cloud_mode()) {
-            bool exists = false;
-            auto st = _fs->exists(file, &exists);
-            DBUG_EXECUTE_IF("DorisFSDirectoryFactory::getDirectory_exists_status_is_not_ok", {
-                st = Status::Error<ErrorCode::INTERNAL_ERROR>(
-                        "debug point: "
-                        "DorisFSDirectoryFactory::getDirectory_exists_status_is_not_ok");
-            })
-            LOG_AND_THROW_IF_ERROR(st, "Get directory exists IO error");
-            if (!exists) {
-                st = _fs->create_directory(file);
-                DBUG_EXECUTE_IF(
-                        "DorisFSDirectoryFactory::getDirectory_create_directory_status_is_not_ok", {
-                            st = Status::Error<ErrorCode::INTERNAL_ERROR>(
-                                    "debug point: "
-                                    "DorisFSDirectoryFactory::getDirectory_create_directory_status_"
-                                    "is_"
-                                    "not_ok");
-                        })
-                LOG_AND_THROW_IF_ERROR(st, "Get directory create directory IO error");
-            }
+        bool exists = false;
+        auto st = _fs->exists(file, &exists);
+        DBUG_EXECUTE_IF("DorisFSDirectoryFactory::getDirectory_exists_status_is_not_ok", {
+            st = Status::Error<ErrorCode::INTERNAL_ERROR>(
+                    "debug point: "
+                    "DorisFSDirectoryFactory::getDirectory_exists_status_is_not_ok");
+        })
+        LOG_AND_THROW_IF_ERROR(st, "Get directory exists IO error");
+        if (!exists) {
+            st = _fs->create_directory(file);
+            DBUG_EXECUTE_IF(
+                    "DorisFSDirectoryFactory::getDirectory_create_directory_status_is_not_ok", {
+                        st = Status::Error<ErrorCode::INTERNAL_ERROR>(
+                                "debug point: "
+                                "DorisFSDirectoryFactory::getDirectory_create_directory_status_"
+                                "is_"
+                                "not_ok");
+                    })
+            LOG_AND_THROW_IF_ERROR(st, "Get directory create directory IO error");
         }
         dir = _CLNEW DorisFSDirectory();
     }