Import React namespace to improve React 17 compatibility with ESM

[scottrippey]

In React 17, useInsertionEffect does not exist.
In #10, we are now exporting ESM, so import { useInsertionEffect } fails with React 17. Reported as #11.

This PR fixes that by importing the React namespace instead.

Considerations: does this defeat the purpose of building as ESM? Does this disable "tree shaking"? I don't imagine that React can be tree-shaken, so probably not.

[shkreios]

@scottrippey AFAIK react itself only has a cjs output and is not tree shakable.
I tested 0.9.4 and the version of this pr both in react 17, 18 & preact all using vite, but couldn't get any error.
I added a comment to the #11 to ask in which dev env the error came up.
For now, I think the solution should be fine, but maybe it's worth looking at the internal package from emotion/react @emotion/use-insertion-effect-with-fallbacks (see code here).

They are using string interpolation to access useInsertionEffect, probably because some bundlers would try to optimize the access, which would cause errors.

[scottrippey]

Published as 0.9.5!