Test docCommentTemplate for prototype methods (#31477)

This works in 3.5, but didn't in 3.2. Adding a test to make sure it
stays working.

tests/cases/fourslash/docCommentTemplatePrototypeMethod.ts

@@ -0,0 +1,15 @@
+/// <reference path='fourslash.ts' />
+// @Filename: foo.js
+
+/////** @class */
+////function C() { }
+/////*above*/
+////C.prototype.method = /*next*/ function (p) {}
+
+for (const marker of test.markerNames()) {
+    verify.docCommentTemplateAt(marker, 8,
+`/**
+ * 
+ * @param {any} p
+ */`);
+}