[draft] Use Babel to transpile JSX instead of TypeScript (#573)

It seems like we're allowing TypeScript to transpile JSX, when we could be allowing Babel to do so. Having TypeScript pass-through JSX to babel would mean we only have to support it being configurable in one place.

(hoping this fixes #564)

Co-authored-by: Leah <me@hrmny.sh>
Co-authored-by: Leah <github.leah@hrmny.sh>

src/index.js

@@ -468,7 +468,7 @@ function createConfig(options, entry, format, writeMeta) {
 									sourceMap: options.sourcemap,
 									declaration: true,
 									declarationDir: getDeclarationDir({ options, pkg }),
-									jsx: 'react',
+									jsx: 'preserve',
 									jsxFactory:
 										// TypeScript fails to resolve Fragments when jsxFactory
 										// is set, even when it's the same as the default value.