Use vscode/@types for most extension samples

Fixes #180

Changes from using `vscode` to `@types/vscode` for the majority of extension samples. The `@types/vscode` package is much smaller and does not pull in any dependencies.

Other changes:

- Remove so empty test files
- Bump engine versions to match @types/vscode versions
- Use `npm run compile` for most `vscode:prepublish` scripts