Optionally show fixes when using --features ecosystem_ci with cargo and --show-fixes at runtime (#4191)

* Generate fixes when using --show-fixes

Example command: `cargo run --bin ruff -- --no-cache --select F401
--show-source --show-fixes
crates/ruff/resources/test/fixtures/pyflakes/F401_9.py`

Before, `--show-fixes` was ignored:

```
crates/ruff/resources/test/fixtures/pyflakes/F401_9.py:4:22: F401 [*] `foo.baz` imported but unused
  |
4 | __all__ = ("bar",)
5 | from foo import bar, baz
  |                      ^^^ F401
  |
  = help: Remove unused import: `foo.baz`

Found 1 error.
[*] 1 potentially fixable with the --fix option.
```

After:

```
crates/ruff/resources/test/fixtures/pyflakes/F401_9.py:4:22: F401 [*] `foo.baz` imported but unused
  |
4 | __all__ = ("bar",)
5 | from foo import bar, baz
  |                      ^^^ F401
  |
  = help: Remove unused import: `foo.baz`

ℹ Suggested fix
1 1 | """Test: late-binding of `__all__`."""
2 2 |
3 3 | __all__ = ("bar",)
4   |-from foo import bar, baz
  4 |+from foo import bar

Found 1 error.
[*] 1 potentially fixable with the --fix option.
```

* Add `--format ecosystem-ci`

* cargo dev generate-all

* Put behind cargo feature

* Regenerate docs

* Don't test ecosystem_ci feature on CI

* Use top level flag instead

* Fix

* Simplify code based on #4191

* Remove old TODO comment

crates/ruff_cli/src/args.rs

@@ -291,6 +291,10 @@ pub struct CheckArgs {
         conflicts_with = "watch",
     )]
     pub show_settings: bool,
+    /// Dev-only argument to show fixes
+    #[cfg(feature = "ecosystem_ci")]
+    #[arg(long, hide = true)]
+    pub ecosystem_ci: bool,
 }
 
 #[derive(Debug, Clone, Copy, clap::ValueEnum)]