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/tsconfig.json

@@ -6,6 +6,7 @@
 	"include": [
 		"src/**/*",
 		"../../src/vscode-dts/vscode.d.ts",
-		"../../src/vscode-dts/vscode.proposed.documentPaste.d.ts"
+		"../../src/vscode-dts/vscode.proposed.documentPaste.d.ts",
+		"../../src/vscode-dts/vscode.proposed.dropMetadata.d.ts"
 	]
 }