Setup automatic DX tests for Hilla

[platosha]

After introducing React support, we encountered many issues with autocomplete and import suggestions for the components. Many things have effect on the TypeScript IDE behavior for Hilla applications, including:

• package.json and tsconfig.json contents
• npm install behavior and the resulting contents of the node_modules directory
• the version of TypeScript used from the IDE
• Hilla libraries, components, and generated output

In order to ensure that the factors above stay in alignment and together provide a good developer experience for the Hilla starters, let us setup automatic IT tests for Hilla starters behavior with TypeScript IDEs.

There are several ways to tackle this:

• End-to-end testing using VS Code for the web
• Integration tests directly asserting TypeScript Language Server output.

[marcushellberg]

A note on the above: let's make sure we run tests on Windows+Linux+Mac

[marcushellberg]

In addition to automatic tests, I think it would be good to add a manual test before bigger releases (major and minor), where a developer creates a project using the CLI, then creates a defined application without copy-pasting to catch errors like the ones we've had with auto-complete where copypasted code works, but the DX is broken.