Rollup merge of #128377 - veera-sivarajan:fix-128249, r=davidtwco

Fix ICE Caused by Incorrectly Delaying E0107

Fixes  #128249

For the following code:
```rust
trait Foo<T> {}
impl Foo<T: Default> for u8 {}
```
#126054 added some logic to delay emitting E0107 as the names of associated type `T` in the impl header and generic parameter `T` in `trait Foo` match.

But it failed to ensure whether such unexpected associated type bounds are coming from a impl block header. This caused an ICE as the compiler was delaying E0107 for code like:
```rust
trait Trait<Type> {
    type Type;

    fn method(&self) -> impl Trait<Type: '_>;
}
```
because it assumed the associated type bound `Type: '_` is for the generic parameter `Type` in `trait Trait` since the names are same.

This PR adds a check to ensure that E0107 is delayed only in the context of impl block header.

compiler/rustc_hir/src/hir.rs

@@ -3700,6 +3700,11 @@ impl<'hir> OwnerNode<'hir> {
         }
     }
 
+    /// Check if node is an impl block.
+    pub fn is_impl_block(&self) -> bool {
+        matches!(self, OwnerNode::Item(Item { kind: ItemKind::Impl(_), .. }))
+    }
+
     expect_methods_self! {
         expect_item,         &'hir Item<'hir>,        OwnerNode::Item(n),        n;
         expect_foreign_item, &'hir ForeignItem<'hir>, OwnerNode::ForeignItem(n), n;