fix(packages): add index.js in /solid and /react (#5863)

* Rename swiper-solid.js and swiper-react.js to index.js

This way the following code is valid:
```js
// With SolidJS
import { Swiper } from "swiper/solid"
// With React
import { Swiper } from "swiper/react"
```

* Allow both types of imports

src/react/index.d.ts

@@ -0,0 +1 @@
+export * from './swiper-react';

src/react/index.js

@@ -0,0 +1 @@
+export * from './swiper-react.js';

src/react/swiper-react.d.ts

@@ -1,6 +1,6 @@
 import * as React from 'react';
 
-import { SwiperOptions, Swiper as SwiperClass } from '../types/';
+import { SwiperOptions, Swiper as SwiperClass } from '../types';
 
 interface SwiperProps extends SwiperOptions {
   /**

src/solid/index.d.ts

@@ -0,0 +1 @@
+export * from './swiper-solid';

src/solid/index.js

@@ -0,0 +1 @@
+export * from './swiper-solid.js';