refactor: Introduce crates folder (#2088)

This PR introduces a new `crates` directory and moves all "product" crates into that folder. 

Part of #2059.

crates/ruff_dev/src/generate_cli_help.rs

@@ -0,0 +1,49 @@
+//! Generate CLI help.
+#![allow(clippy::print_stdout, clippy::print_stderr)]
+
+use crate::utils::replace_readme_section;
+use anyhow::Result;
+use std::str;
+
+const COMMAND_HELP_BEGIN_PRAGMA: &str = "<!-- Begin auto-generated command help. -->\n";
+const COMMAND_HELP_END_PRAGMA: &str = "<!-- End auto-generated command help. -->";
+
+const SUBCOMMAND_HELP_BEGIN_PRAGMA: &str = "<!-- Begin auto-generated subcommand help. -->\n";
+const SUBCOMMAND_HELP_END_PRAGMA: &str = "<!-- End auto-generated subcommand help. -->";
+
+#[derive(clap::Args)]
+pub struct Args {
+    /// Write the generated help to stdout (rather than to `README.md`).
+    #[arg(long)]
+    pub(crate) dry_run: bool,
+}
+
+fn trim_lines(s: &str) -> String {
+    s.lines().map(str::trim_end).collect::<Vec<_>>().join("\n")
+}
+
+pub fn main(args: &Args) -> Result<()> {
+    // Generate `ruff help`.
+    let command_help = trim_lines(ruff_cli::command_help().trim());
+
+    // Generate `ruff help check`.
+    let subcommand_help = trim_lines(ruff_cli::subcommand_help().trim());
+
+    if args.dry_run {
+        print!("{command_help}");
+        print!("{subcommand_help}");
+    } else {
+        replace_readme_section(
+            &format!("```text\n{command_help}\n```\n\n"),
+            COMMAND_HELP_BEGIN_PRAGMA,
+            COMMAND_HELP_END_PRAGMA,
+        )?;
+        replace_readme_section(
+            &format!("```text\n{subcommand_help}\n```\n\n"),
+            SUBCOMMAND_HELP_BEGIN_PRAGMA,
+            SUBCOMMAND_HELP_END_PRAGMA,
+        )?;
+    }
+
+    Ok(())
+}