Function isIndexSignature

test/fixtures/snapshot/typescript.js:33603–33605

()

            return withJSDoc(finishNode(node, pos), hasJSDoc);
        }
        function isIndexSignature() {
            return token() === 22 /* SyntaxKind.OpenBracketToken */ && lookAhead(isUnambiguouslyIndexSignature);
        }
        function isUnambiguouslyIndexSignature() {
            // The only allowed sequence is:
            //