Conditional exports demos

Folders:

• /package - Simple isomorphic package with one entrypoint for node, and one for workerd
• /demo-package - Demo project showing how importing this package from Npm works perfectly
• /demo-folder-as-package - Demo project showing how importing the package from a folder via package.json also works perfectly (to represent monorepo setups)
• /demo-folder - Demo project showing how importing directly via the path does not work