[commit] Add support for commonjs

We previously always generated import statements for any modules that had to be required, notably the `import {c} from 'react/compiler-runtime'` for the memo cache function. However, this obviously doesn't work when the source is using commonjs. Now we check the sourceType of the module and generate require() statements if the source type is 'script'.

I initially explored using https://babeljs.io/docs/babel-helper-module-imports, but the API design was unfortunately not flexible enough for our use-case. Specifically, our pipeline is as follows:
* Compile individual functions. Generate candidate imports, pre-allocating the local names for those imports.
* If the file is compiled successfully, actually add the imports to the program.

Ie we need to pre-allocate identifier names for the imports before we add them to the program — but that isn't supported by babel-helper-module-imports. So instead we generate our own require() calls if the sourceType is script.