docs(transformer): add documentation for optional-catch-binding plu…

…gin (#5064)

follow-up #4881

crates/oxc_transformer/src/es2019/optional_catch_binding.rs

@@ -1,3 +1,37 @@
+//! ES2019: Optional Catch Binding
+//!
+//! This plugin transform catch clause without parameter to add a parameter called `unused` in catch clause.
+//!
+//! > This plugin is included in `preset-env`, in ES2019
+//!
+//! ## Example
+//!
+//! Input:
+//! ```js
+//! try {
+//!   throw 0;
+//! } catch {
+//!   doSomethingWhichDoesNotCareAboutTheValueThrown();
+//! }
+//! ```
+//!
+//! Output:
+//! ```js
+//! try {
+//!   throw 0;
+//! } catch (_unused) {
+//!   doSomethingWhichDoesNotCareAboutTheValueThrown();
+//! }
+//! ```
+//!
+//! ## Implementation
+//!
+//! Implementation based on [@babel/plugin-transform-optional-catch-binding](https://babel.dev/docs/babel-plugin-transform-optional-catch-binding).
+//!
+//! ## References:
+//! * Babel plugin implementation: <https://github.com/babel/babel/tree/main/packages/babel-plugin-transform-optional-catch-binding>
+//! * Optional catch binding TC39 proposal: <https://github.com/tc39/proposal-optional-catch-binding>
+
 use std::cell::Cell;
 
 use oxc_ast::ast::*;
@@ -7,11 +41,6 @@ use oxc_traverse::TraverseCtx;
 
 use crate::context::Ctx;
 
-/// ES2019: Optional Catch Binding
-///
-/// References:
-/// * <https://babel.dev/docs/babel-plugin-transform-optional-catch-binding>
-/// * <https://github.com/babel/babel/tree/main/packages/babel-plugin-transform-optional-catch-binding>
 pub struct OptionalCatchBinding<'a> {
     _ctx: Ctx<'a>,
 }
@@ -22,16 +51,6 @@ impl<'a> OptionalCatchBinding<'a> {
     }
 
     /// If CatchClause has no param, add a parameter called `unused`.
-    ///
-    /// ```ts
-    /// try {}
-    /// catch {}
-    /// ```
-    /// too
-    /// ```ts
-    /// try {}
-    /// catch (_unused) {}
-    /// ```
     #[allow(clippy::unused_self)]
     pub fn transform_catch_clause(&self, clause: &mut CatchClause<'a>, ctx: &mut TraverseCtx<'a>) {
         if clause.param.is_some() {