[JS/TS] fix flatbuffers default export (google#6123)

* [TS/JS] Export flatbuffers namespace as default export

* [TS/JS] Fully qualified name

* Export as default and named

Author: bjornharrtell

package.json

@@ -9,7 +9,7 @@
     "mjs/*.d.ts",
     "ts/*.ts"
   ],
-  "main": "js/flatbuffers",
+  "main": "js/flatbuffers.js",
   "module": "mjs/index.mjs",
   "directories": {
     "doc": "docs",

ts/flatbuffers.ts

@@ -31,3 +31,4 @@ export namespace flatbuffers {
     export const ByteBuffer = ByteBufferClass;
 }
 
+export default flatbuffers;