chore: export default shimmer function

Author: Joozty

experimental/packages/opentelemetry-instrumentation/src/index.ts

@@ -33,4 +33,4 @@ export {
   safeExecuteInTheMiddleAsync,
 } from './utils';
 export { SemconvStability, semconvStabilityFromStr } from './semconvStability';
-export * from './shimmer'
+export { default as shimmer } from './shimmer';