prepareDocumentPaste
Optional method invoked after the user copies from a text editor.
This allows the provider to attach metadata about the copied text to the DataTransfer. This data transfer is then passed back to providers in {@linkcode provideDocumentPasteEdits}.
Note that currently any changes to the {@linkcode DataTransfer} are isolated to the current editor window. This means that any added metadata cannot be seen by other editor windows or by other applications.
Return
Optional thenable that resolves when all changes to the dataTransfer are complete.
Parameters
Text document where the copy took place.
Ranges being copied in {@linkcode document}.
The data transfer associated with the copy. You can store additional values on this for later use in {@linkcode provideDocumentPasteEdits}. This object is only valid for the duration of this method.
A cancellation token.