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> {

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

@@ -38,12 +38,23 @@ export function registerDropIntoEditorSupport(selector: vscode.DocumentSelector)
 			}
 
 			const snippet = await tryGetUriListSnippet(document, dataTransfer, token);
-			return snippet ? new vscode.DocumentDropEdit(snippet) : undefined;
+			if (!snippet) {
+				return undefined;
+			}
+
+			const edit = new vscode.DocumentDropEdit(snippet.snippet);
+			edit.label = snippet.label;
+			return edit;
 		}
+	}, {
+		id: 'vscode.markdown.insertLink',
+		dropMimeTypes: [
+			'text/uri-list'
+		]
 	});
 }
 
-export async function tryGetUriListSnippet(document: vscode.TextDocument, dataTransfer: vscode.DataTransfer, token: vscode.CancellationToken): Promise<vscode.SnippetString | undefined> {
+export async function tryGetUriListSnippet(document: vscode.TextDocument, dataTransfer: vscode.DataTransfer, token: vscode.CancellationToken): Promise<{ snippet: vscode.SnippetString; label: string } | undefined> {
 	const urlList = await dataTransfer.get('text/uri-list')?.asString();
 	if (!urlList || token.isCancellationRequested) {
 		return undefined;
@@ -58,7 +69,17 @@ export async function tryGetUriListSnippet(document: vscode.TextDocument, dataTr
 		}
 	}
 
-	return createUriListSnippet(document, uris);
+	const snippet = createUriListSnippet(document, uris);
+	if (!snippet) {
+		return undefined;
+	}
+
+	return {
+		snippet: snippet,
+		label: uris.length > 1
+			? vscode.l10n.t('Insert uri links')
+			: vscode.l10n.t('Insert uri link')
+	};
 }
 
 interface UriListSnippetOptions {