This PR extracts Dockerfile support into an extension and removes the built-in Dockerfile support from Zed. There's already an existing [Dockerfile extension](https://github.com/d1y/dockerfile.zed) that was just missing language server support. Language server support is being added to that extension in https://github.com/d1y/dockerfile.zed/pull/2. Release Notes: - Removed built-in support for Dockerfile, in favor of making it available as an extension. The Dockerfile extension will be suggested for download when you open a `Dockerfile`.