Fix doc comment template on assignment expressions (microsoft#38032)

Author: andrewbranch

src/services/jsDoc.ts

@@ -363,6 +363,8 @@ namespace ts.JsDoc {
                 // want to give back a JSDoc template for the 'b' or 'c' in 'namespace a.b.c { }'.
                 return commentOwner.parent.kind === SyntaxKind.ModuleDeclaration ? undefined : { commentOwner };
 
+            case SyntaxKind.ExpressionStatement:
+                return getCommentOwnerInfoWorker((commentOwner as ExpressionStatement).expression);
             case SyntaxKind.BinaryExpression: {
                 const be = commentOwner as BinaryExpression;
                 if (getAssignmentDeclarationKind(be) === AssignmentDeclarationKind.None) {

tests/cases/fourslash/docCommentTemplateExportAssignmentJS.ts

@@ -0,0 +1,15 @@
+/// <reference path='fourslash.ts' />
+
+// @allowJs: true
+// @checkJs: true
+
+// @Filename: index.js
+//// /** /**/ */
+//// exports.foo = (a) => {};
+
+
+verify.docCommentTemplateAt("", 8,
+`/**
+ * 
+ * @param {any} a
+ */`);