New properties in Storage.Pickers - SuggestedDefaultFolder, FileTypeChoices

[DinahK-2SO]

An implementation of

• API review for new properties in Storage.Pickers - SuggestedDefaultFolder, FileTypeChoices #5771

This pull request adds new functionality to the Storage Pickers API, introducing a SuggestedDefaultFolder property to FileOpenPicker, FileSavePicker, and FolderPicker, and enhances file type filtering in FileOpenPicker with a new FileTypeChoices property. It also refactors internal handling of folder and filter properties to provide better validation and precedence logic.

API Additions and Enhancements:

• Added SuggestedDefaultFolder property (getter/setter) to FileOpenPicker, FileSavePicker, and FolderPicker, allowing callers to specify a default folder path. This property takes precedence over SuggestedStartLocation when both are set. (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
• Introduced FileTypeChoices property to FileOpenPicker, allowing more granular file type filtering by mapping display names to lists of extensions. (1, 2, 3, 4)

Internal Logic and Validation Improvements:

• Refactored folder path validation by replacing ValidateSuggestedFolder with a more general ValidateFolderPathProperty, which accepts the property name for clearer error messages. (1, 2, 3)
• Updated picker parameter logic so that SuggestedDefaultFolder takes precedence over SuggestedStartLocation, and FileTypeChoices takes precedence over FileTypeFilter in FileOpenPicker. (1, 2, 3, 4)

Supporting Infrastructure and Versioning:

• Updated the IDL contract version to 1.9 and annotated the new properties with the appropriate contract version to ensure compatibility and feature gating. (1, 2, 3, 4)
• Improved internal filter handling in PickerParameters, including the ability to union file type choices for the "All Files" category and to process both FileTypeFilter and FileTypeChoices appropriately. (1, 2)

These changes provide app developers with more control over picker initialization and file type filtering, while improving validation and internal consistency.