demo/typescript.js
function getJsxAttributePropertySymbol(attrib) {
            var attributesType = getJsxElementAttributesType(attrib.parent);
            var prop = getPropertyOfType(attributesType, attrib.name.text);
            return prop || unknownSymbol;
        }
function getJsxAttributePropertySymbol(attrib) {
            var attributesType = getJsxElementAttributesType(attrib.parent);
            var prop = getPropertyOfType(attributesType, attrib.name.text);
            return prop || unknownSymbol;
        }
Given a JSX attribute, returns the symbol for the corresponds property
of the element attributes type. Will return unknownSymbol for attributes
that have no matching element attributes type property.