chore: use Node16 and add extensions to all relative imports

[AdrianGonz97]

This PR is a prerequisite to adding the adder templates into the repo.

While working on migrating over the templates, I noticed that none of the types from the core package were resolving correctly in the adder templates due to our lack of file extensions in relative imports (since we had moduleResolution set to Bundler, it allowed us to have a mix of imports with and without extensions, causing things to break for projects that use moduleResolution: Node16).

Since this is will also be needed for Rolldown in the future, we might as well get this out of the way

[pkg-pr-new]

Open in Stackblitz

pnpm add https://pkg.pr.new/sveltejs/cli/@svelte-cli/ast-manipulation@28

pnpm add https://pkg.pr.new/sveltejs/cli/@svelte-cli/ast-tooling@28

pnpm add https://pkg.pr.new/sveltejs/cli/sv@28

pnpm add https://pkg.pr.new/sveltejs/cli/@svelte-cli/core@28

commit: 95e9dc1

[benmccann]

thank goodness for allowImportingTsExtensions!