Support for the React 17 JSX Transform.

I am running into an error which I suspect to be caused by the release of React 17.
@see https://reactjs.org/blog/2020/09/22/introducing-the-new-jsx-transform.html

Typescript 4.1 followed by supporting as well the new `JSX` Factory

However when I run `microbundle-crl --no-compress --format modern, cjs` I get the following errors.

```bash
rpt2: config error TS6046: Argument for '--jsx' option must be: 'preserve', 'react-native', 'react'.

(rpt2 plugin) Error:.../Select/index.ts(1,20): semantic error TS6142: Module './Select' was resolved to '.../Select/Select.tsx', but '--jsx' is not set.
Error: .../Select/index.ts(1,20): semantic error TS6142: Module './Select' was resolved to '.../Select.tsx', but '--jsx' is not set.
```
I have indeed `jsx: "react-jsx"` in my `tsconfig.js`

Is there a quick solution for this?
Thanks

Start by running the reported microbundle-crl command and inspect tsconfig.js alongside the rpt2/TypeScript configuration it uses. Reproduce the errors for Select/index.ts and Select/Select.tsx; done means the React 17 JSX transform is accepted and the build completes without TS6046 or TS6142.

Escrita pelo modelo de indexação a partir do texto da issue.