build: fix reexports to be SystemJS compatible after transpilation

spec/systemjs-compatibility-spec.ts

@@ -0,0 +1,7 @@
+// all these imports verify that our ESM imports and exports are SystemJS compatible after transpilation
+// this is done by relying on the tsc type-checker configured with "moduleResolution" set to "classic"
+import * as rxjs from '../src/index';
+import * as rxjsAjax from '../src/ajax';
+import * as rxjsOperators from '../src/operators';
+import * as rxjsTesting from '../src/testing';
+import * as rxjsWebsocket from '../src/websocket';

src/ajax.ts

@@ -0,0 +1 @@
+export * from './ajax/index';

src/internal/Rx.ts

@@ -176,7 +176,7 @@ import { rxSubscriber } from './symbol/rxSubscriber';
 import { iterator } from './symbol/iterator';
 import { observable } from './symbol/observable';
 
-import * as _operators from './operators';
+import * as _operators from './operators/index';
 
 export const operators = _operators;
 

src/operators.ts

@@ -0,0 +1 @@
+export * from './operators/index';

src/testing.ts

@@ -0,0 +1 @@
+export * from './testing/index';

src/websocket.ts

@@ -0,0 +1 @@
+export * from './websocket/index';

tsconfig.json

@@ -8,7 +8,7 @@
     "noImplicitReturns": true,
     "noImplicitThis": true,
     "suppressImplicitAnyIndexErrors": true,
-    "moduleResolution": "node",
+    "moduleResolution": "classic", // we intentionally use "classic" module resolution to be SystemJS-compatible after transpilation
     "stripInternal": true,
     "target": "es5",
     "outDir": "./.out",