Update drop metadata proposal (#179918)

- Makes `dropMimeTypes` required
- Prefix the actual `id` used internally with the extension id
- Allow wildcard mime types, such as `image/*`

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

@@ -47,7 +47,7 @@ export function registerDropIntoEditorSupport(selector: vscode.DocumentSelector)
 			return edit;
 		}
 	}, {
-		id: 'vscode.markdown.insertLink',
+		id: 'insertLink',
 		dropMimeTypes: [
 			'text/uri-list'
 		]