PAINTROID-782 : Use file picker for choosing file saving location

[Nithish-Sri-Ram]

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New Features and Enhancements

• Integrated file_picker package to allow users to choose a directory for saving images or projects.
• Added functionality to prompt users with a directory picker when saving.
• Updated image metadata handling to include the selected directory path, replacing the default emulated storage behavior.
  Improved user experience by offering flexibility and control over file-saving locations.

782.mp4

Refactorings and Bug Fixes

• Adjusted _dismissDialogWithData logic to support file picker integration.
• Refactored image saving logic to ensure compatibility with new directory selection.

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