fix merging snippets

increase nesting level of the snippet based on how many snippets need to be merged instead an arbitrary value of 10.

Author: superle3

src/vs/editor/contrib/snippet/browser/snippetSession.ts

@@ -289,7 +289,9 @@ export class OneSnippet {
 	merge(others: OneSnippet[]): void {
 
 		const model = this._editor.getModel();
-		this._nestingLevel *= 10;
+		this._nestingLevel *= Math.max(
+			...others.map(o => o._snippet.placeholderInfo.last?.index || 8)
+		) + 2;
 
 		this._editor.changeDecorations(accessor => {