function getJsxGlobalElementClassType() {
            if (!jsxElementClassType) {
                jsxElementClassType = getExportedTypeFromNamespace(JsxNames.JSX, JsxNames.ElementClass);
            }
            return jsxElementClassType;
        }
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.