Make iter::order functions into methods on Iterator

This does cause some breakage due to deficiencies in resolve -
`path::Components` is both an `Iterator` and implements `Eq`, `Ord`,
etc. If one calls e.g. `partial_cmp` on a `Components` and passes a
`&Components` intending to target the `PartialOrd` impl, the compiler
will select the `partial_cmp` from `Iterator` and then error out. I
doubt anyone will run into breakage from `Components` specifically, but
we should see if there are third party types that will run into issues.

`iter::order::equals` wasn't moved to `Iterator` since it's exactly the
same as `iter::order::eq` but with an `Eq` instead of `PartialEq` bound,
which doensn't seem very useful.

I also updated `le`, `gt`, etc to use `partial_cmp` which lets us drop
the extra `PartialEq` bound.

cc #27737

src/libstd/path.rs

@@ -882,7 +882,7 @@ impl<'a> DoubleEndedIterator for Components<'a> {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a> cmp::PartialEq for Components<'a> {
     fn eq(&self, other: &Components<'a>) -> bool {
-        iter::order::eq(self.clone(), other.clone())
+        Iterator::eq(self.clone(), other.clone())
     }
 }
 
@@ -892,14 +892,14 @@ impl<'a> cmp::Eq for Components<'a> {}
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a> cmp::PartialOrd for Components<'a> {
     fn partial_cmp(&self, other: &Components<'a>) -> Option<cmp::Ordering> {
-        iter::order::partial_cmp(self.clone(), other.clone())
+        Iterator::partial_cmp(self.clone(), other.clone())
     }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a> cmp::Ord for Components<'a> {
     fn cmp(&self, other: &Components<'a>) -> cmp::Ordering {
-        iter::order::cmp(self.clone(), other.clone())
+        Iterator::cmp(self.clone(), other.clone())
     }
 }
 
@@ -1162,14 +1162,14 @@ impl cmp::Eq for PathBuf {}
 #[stable(feature = "rust1", since = "1.0.0")]
 impl cmp::PartialOrd for PathBuf {
     fn partial_cmp(&self, other: &PathBuf) -> Option<cmp::Ordering> {
-        self.components().partial_cmp(&other.components())
+        self.components().partial_cmp(other.components())
     }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl cmp::Ord for PathBuf {
     fn cmp(&self, other: &PathBuf) -> cmp::Ordering {
-        self.components().cmp(&other.components())
+        self.components().cmp(other.components())
     }
 }
 
@@ -1691,7 +1691,7 @@ impl<'a> fmt::Display for Display<'a> {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl cmp::PartialEq for Path {
     fn eq(&self, other: &Path) -> bool {
-        iter::order::eq(self.components(), other.components())
+        self.components().eq(other.components())
     }
 }
 
@@ -1701,14 +1701,14 @@ impl cmp::Eq for Path {}
 #[stable(feature = "rust1", since = "1.0.0")]
 impl cmp::PartialOrd for Path {
     fn partial_cmp(&self, other: &Path) -> Option<cmp::Ordering> {
-        self.components().partial_cmp(&other.components())
+        self.components().partial_cmp(other.components())
     }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl cmp::Ord for Path {
     fn cmp(&self, other: &Path) -> cmp::Ordering {
-        self.components().cmp(&other.components())
+        self.components().cmp(other.components())
     }
 }