Standardize text/uri-list handling (#152756)

This creates a common set of functions for creating and parsing the `text/uri-list` mime type. As part of this, I also aligned us with the standard, which uses `\r\n` between lines instead of just `\n`

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

@@ -44,7 +44,7 @@ export async function tryGetUriListSnippet(document: vscode.TextDocument, dataTr
 	}
 
 	const uris: vscode.Uri[] = [];
-	for (const resource of urlList.split('\n')) {
+	for (const resource of urlList.split('\r\n')) {
 		try {
 			uris.push(vscode.Uri.parse(resource));
 		} catch {