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

[TiagoCavalcante]

This way the following code is valid:

// With SolidJS
import { Swiper } from "swiper/solid"
// With React
import { Swiper } from "swiper/react"

[TiagoCavalcante]

In my last commit, instead of renaming, I created a file that exports everything from swiper-solid, to keep backward compatibility.

[nolimits4web]

Merged, thanks!