Feat: Auto output directory naming and removed confirmation pop-up

[Chapoly1305]

This pull request introduces improvements to the handling of output directories in the PDFsam application, focusing on better user experience and robustness when specifying or creating output folders. The main enhancements include a new request class for setting output directories, improved UI feedback when a directory will be created, automatic directory creation if it does not exist, and consistent handling across multiple tools.

As illustrated, when target directory is not existing, a green hint will be given. At run, no more pop-up will be given, improving continuous user experience.

Tested on macOS.

Key changes:

Output Directory Handling and API:

• Added a new SetOutputDirectoryRequest record in org.pdfsam.model.ui to encapsulate requests for setting output directories, including support for fallback behavior and utility methods for generating directory names based on input files.
• Updated SingleSelectionPane to broadcast a fallback output directory request when a PDF is loaded, ensuring downstream components can respond appropriately. [1] [2]

UI/UX Enhancements:

• Enhanced BrowsableOutputDirectoryField to display an info label when the specified output directory does not exist, informing the user that the folder will be created. [1] [2]
• The info label is now added to the DestinationPane UI when using a BrowsableOutputDirectoryField.

Robustness and Consistency:

• Modified BrowsableOutputDirectoryField to automatically create the output directory if it does not exist, and to handle errors gracefully with user feedback.
• Updated tool modules (SplitTool, SplitByBookmarksTool, SplitBySizeTool) to instantiate BrowsableOutputDirectoryField with the tool ID for consistent event handling and tool binding. [1] [2] [3]

These changes collectively improve the reliability and user-friendliness of output directory selection across the application.