Fix drop priorities for notebooks (microsoft#182209)

For copy paste, I added logic to prefer using the text content if there's both `image/*` and `text/*` content in the clipboard

This however I also incorrectly applied this logic when dropping. In those cases, we instead want to prefer the image data (at least we do in the case of dragging and dropping from VS Code's explorer)

Author: mjbvz

extensions/ipynb/src/notebookImagePaste.ts

@@ -49,6 +49,8 @@ class DropOrPasteEditProvider implements vscode.DocumentPasteEditProvider, vscod
 
 	private readonly id = 'insertAttachment';
 
+	private readonly defaultPriority = 5;
+
 	async provideDocumentPasteEdits(
 		document: vscode.TextDocument,
 		_ranges: readonly vscode.Range[],
@@ -66,7 +68,7 @@ class DropOrPasteEditProvider implements vscode.DocumentPasteEditProvider, vscod
 		}
 
 		const pasteEdit = new vscode.DocumentPasteEdit(insert.insertText, this.id, vscode.l10n.t('Insert Image as Attachment'));
-		pasteEdit.priority = this.getPriority(dataTransfer);
+		pasteEdit.priority = this.getPastePriority(dataTransfer);
 		pasteEdit.additionalEdit = insert.additionalEdit;
 		return pasteEdit;
 	}
@@ -84,20 +86,20 @@ class DropOrPasteEditProvider implements vscode.DocumentPasteEditProvider, vscod
 
 		const dropEdit = new vscode.DocumentDropEdit(insert.insertText);
 		dropEdit.id = this.id;
-		dropEdit.priority = this.getPriority(dataTransfer);
+		dropEdit.priority = this.defaultPriority;
 		dropEdit.additionalEdit = insert.additionalEdit;
 		dropEdit.label = vscode.l10n.t('Insert Image as Attachment');
 		return dropEdit;
 	}
 
-	private getPriority(dataTransfer: vscode.DataTransfer): number {
+	private getPastePriority(dataTransfer: vscode.DataTransfer): number {
 		if (dataTransfer.get('text/plain')) {
 			// Deprioritize in favor of normal text content
 			return -5;
 		}
 
 		// Otherwise boost priority so attachments are preferred
-		return 5;
+		return this.defaultPriority;
 	}
 
 	private async createInsertImageAttachmentEdit(