Improve User Feedback During File Retrieval

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When a user attempts to open a document or file in the Files app from another application (e.g., the Talk app), the Files app may need to perform several operations before the file is displayed:

1. Launch the Files app if it is not already running
2. Retrieve the file if it does not yet exist locally
3. Load and open the file once it becomes available

Depending on device performance or server responsiveness, these operations can take a considerable amount of time (e.g., 90 seconds on slow instances). During this period, the UI currently shows a brief "retrieving" snackbar message, after which no further feedback is visible. This can make the app appear unresponsive or stalled, leading to user confusion.