`deno fmt --check` was broken for CSS, YAML and HTML files.
Before this PR, formatting any of these file types would return a
string, even though the contract in `cli/tools/fmt.rs` is to only return a
string if the formatting changed. This causes wrong flagging of these files
as being badly formatted even though diffs showed nothing (because
they were in fact formatted properly).
Closes https://github.com/denoland/deno/issues/25840
This commits stabilizes CSS, HTML and YAML formatters
in `deno fmt`.
It is no longer required to use either of these flags:
- `--unstable-css`
- `--unstable-html`
- `--unstable-yaml`
Or these `unstable` options in the config file:
- `fmt-css`
- `fmt-html`
- `html-yaml`
