[FR] Add a button for copying the whole document on Android

[mon-jai]

Description

It is currently impossible to copy the entire document. The system's "Select All" button only selects a section in Appflowy.

While users can manually drag and select the whole document to copy the plain text, all formatting (e.g., lists, titles) is lost. This requires users to manually reformat copied content.

Impact

Make it easy to copy and share content (with its intended formatting intact) from the App to other applications or documents.

Additional Context

No response