Add drop feedback UX (#179434)

For #179430

Adds two new UX components:

- An inline progress icon shown when a drop operation takes over 500ms. This replaces the notification. You can click on it to cancel the drop

- Post drop, a drop feedback icon that lets you drop the file in a different way. This lets you drop the file as plain text for instance instead of as a markdown link

extensions/markdown-language-features/src/languageFeatures/copyFiles/copyPaste.ts

@@ -45,7 +45,7 @@ class PasteEditProvider implements vscode.DocumentPasteEditProvider {
 		}
 
 		const snippet = await tryGetUriListSnippet(document, dataTransfer, token);
-		return snippet ? new vscode.DocumentPasteEdit(snippet) : undefined;
+		return snippet ? new vscode.DocumentPasteEdit(snippet.snippet) : undefined;
 	}
 
 	private async _makeCreateImagePasteEdit(document: vscode.TextDocument, file: vscode.DataTransferFile, token: vscode.CancellationToken): Promise<vscode.DocumentPasteEdit | undefined> {