Add test

tests/cases/fourslash/signatureHelpJSX.ts

@@ -0,0 +1,10 @@
+/// <reference path="fourslash.ts" />
+
+//@Filename: test.tsx
+//@jsx: react
+////declare var React: any;
+////const z = <div>{[].map(x => </**/
+
+// This test exists because it used to crash: #31347
+goTo.marker();
+verify.noSignatureHelpForTriggerReason({ kind: "characterTyped", triggerCharacter: "<" });