Add multi-file drop processing

The Load button's file management dialog has a drop target and an Add a file to the filesystem button.

The button opens an OS file browser dialog that accepts selecting multiple modules and indeed processes them properly (adding them to the file system in one operation); however, while the drop target accepts a multi-file drop event, it does not process any but the first module in the selection.

When multiple modules need to be added to a project, the drop target method isn't as convenient without this multi-file drop capability.

從 Load 按鈕的檔案管理對話方塊開始，檢查放置目標的處理方式，並將其與現有的 Add a file to the filesystem 流程進行比較，該流程會處理多個選取的模組。完成標準是：放置多個模組時，應在一次操作中將每個模組都加入專案檔案系統，而不是只加入第一個模組。