use Self alias in self types rather than manually substituting it

library/alloc/src/str.rs

@@ -234,7 +234,7 @@ impl str {
     #[stable(feature = "str_box_extras", since = "1.20.0")]
     #[must_use = "`self` will be dropped if the result is not used"]
     #[inline]
-    pub fn into_boxed_bytes(self: Box<str>) -> Box<[u8]> {
+    pub fn into_boxed_bytes(self: Box<Self>) -> Box<[u8]> {
         self.into()
     }
 
@@ -501,7 +501,7 @@ impl str {
     #[rustc_allow_incoherent_impl]
     #[must_use = "`self` will be dropped if the result is not used"]
     #[inline]
-    pub fn into_string(self: Box<str>) -> String {
+    pub fn into_string(self: Box<Self>) -> String {
         let slice = Box::<[u8]>::from(self);
         unsafe { String::from_utf8_unchecked(slice.into_vec()) }
     }

library/core/src/pin.rs

@@ -1422,7 +1422,7 @@ impl<Ptr: DerefMut> Pin<Ptr> {
     #[stable(feature = "pin_deref_mut", since = "1.84.0")]
     #[must_use = "`self` will be dropped if the result is not used"]
     #[inline(always)]
-    pub fn as_deref_mut(self: Pin<&mut Pin<Ptr>>) -> Pin<&mut Ptr::Target> {
+    pub fn as_deref_mut(self: Pin<&mut Self>) -> Pin<&mut Ptr::Target> {
         // SAFETY: What we're asserting here is that going from
         //
         //     Pin<&mut Pin<Ptr>>

library/std/src/ffi/os_str.rs

@@ -1040,7 +1040,7 @@ impl OsStr {
     /// Converts a <code>[Box]<[OsStr]></code> into an [`OsString`] without copying or allocating.
     #[stable(feature = "into_boxed_os_str", since = "1.20.0")]
     #[must_use = "`self` will be dropped if the result is not used"]
-    pub fn into_os_string(self: Box<OsStr>) -> OsString {
+    pub fn into_os_string(self: Box<Self>) -> OsString {
         let boxed = unsafe { Box::from_raw(Box::into_raw(self) as *mut Slice) };
         OsString { inner: Buf::from_box(boxed) }
     }

library/std/src/path.rs

@@ -3163,7 +3163,7 @@ impl Path {
     /// allocating.
     #[stable(feature = "into_boxed_path", since = "1.20.0")]
     #[must_use = "`self` will be dropped if the result is not used"]
-    pub fn into_path_buf(self: Box<Path>) -> PathBuf {
+    pub fn into_path_buf(self: Box<Self>) -> PathBuf {
         let rw = Box::into_raw(self) as *mut OsStr;
         let inner = unsafe { Box::from_raw(rw) };
         PathBuf { inner: OsString::from(inner) }