fix(traverse): create scope for function nested in class method (#3234)

Fixes a bug in #3229.

The logic to prevent a duplicate scope being created for a `Function` which is a `MethodDefinition` would also stop a scope being created for inner function in:

```rs
class X {
  foo() {
    function bar() {}
  }
}
```

or

```rs
class X {
  foo( bar = function() {} ) {}
}
```

This PR fixes that. This change also allows removing `ScopeFlags::Method` which #3229 added.

crates/oxc_ast/src/ast/js.rs

@@ -2133,8 +2133,10 @@ pub struct BindingRestElement<'a> {
 /// Function Definitions
 #[visited_node(
     scope(ScopeFlags::Function),
-    // Don't create a 2nd scope if `MethodDefinition` already created one
-    scope_if((ctx.scope() & ScopeFlags::Modifiers).is_empty()),
+    // Don't create scope if this is a method - `MethodDefinition` already created one.
+    // `ctx.ancestor(2).unwrap()` not `ctx.parent()` because this code is inserted
+    // into `walk_function` *after* `Function` is added to stack.
+    scope_if(matches!(ctx.ancestor(2).unwrap(), Ancestor::MethodDefinitionValue(_))),
     strict_if(self.body.as_ref().is_some_and(|body| body.has_use_strict_directive()))
 )]
 #[derive(Debug, Hash)]
@@ -2586,7 +2588,7 @@ impl MethodDefinitionKind {
     pub fn scope_flags(self) -> ScopeFlags {
         match self {
             Self::Constructor => ScopeFlags::Constructor,
-            Self::Method => ScopeFlags::Method,
+            Self::Method => ScopeFlags::empty(),
             Self::Get => ScopeFlags::GetAccessor,
             Self::Set => ScopeFlags::SetAccessor,
         }

crates/oxc_syntax/src/scope.rs

@@ -23,11 +23,8 @@ bitflags! {
         const Constructor      = 1 << 6;
         const GetAccessor      = 1 << 7;
         const SetAccessor      = 1 << 8;
-        // Only used in `Traverse`
-        const Method           = 1 << 9;
         const Var = Self::Top.bits() | Self::Function.bits() | Self::ClassStaticBlock.bits() | Self::TsModuleBlock.bits();
-        const Modifiers = Self::Constructor.bits() | Self::GetAccessor.bits()
-            | Self::SetAccessor.bits() | Self::Method.bits();
+        const Modifiers = Self::Constructor.bits() | Self::GetAccessor.bits() | Self::SetAccessor.bits();
     }
 }
 

crates/oxc_traverse/src/walk.rs

@@ -2228,7 +2228,7 @@ pub(crate) unsafe fn walk_function<'a, Tr: Traverse<'a>>(
 ) {
     traverser.enter_function(&mut *node, ctx);
     ctx.push_stack(Ancestor::FunctionId(ancestor::FunctionWithoutId(node)));
-    let has_scope = (ctx.scope() & ScopeFlags::Modifiers).is_empty();
+    let has_scope = matches!(ctx.ancestor(2).unwrap(), Ancestor::MethodDefinitionValue(_));
     if has_scope {
         ctx.push_scope_stack(
             ScopeFlags::Function.with_strict_mode(