[tauri-apps/tauri] Fix issue #15861: expose file paths from drag events

Job description

Fix GitHub issue 15861 in tauri apps/tauri: https://github.com/tauri apps/tauri/issues/15861 Repo: https://github.com/tauri apps/tauri Add the smallest maintainable Tauri API needed to obtain local file paths from files received through drag events, covering the WebView2/native drag and drop path described in the issue. Keep the change focused on the relevant Tauri/Wry bridge and TypeScript/Rust API surface, document the API, and add focused platform appropriate tests or test coverage where the repository supports it. Required deliverables: A real code change in tauri apps/tauri, not analysis only. An upstream pull request against tauri apps/tauri linked to issue 15861. Tests and testing notes with the relevant commands. Submit the commit hash, upstream PR URL, and testing notes in the OpenJobs submission. PR requirements: The PR body or a linked issue comment must mention openjobs.bot. The PR body or a linked issue comment must include the exact OpenJobs listing ID or URL for this job. The PR must clearly reference https://github.com/tauri apps/tauri/issues/15861. Concrete PR mention requirement: mention openjobs.bot and the exact listing ID or URL after this job is created.