EscapeUnicode and EscapeDefault are ExactSizeIterators

In rust-lang#28662, `size_hint` was made exact for `EscapeUnicode` and
`EscapeDefault`, but neither was marked as `ExactSizeIterator`.

src/libcore/char.rs

@@ -483,6 +483,9 @@ impl Iterator for EscapeUnicode {
     }
 }
 
+#[stable(feature = "exact_size_escape", since = "1.11.0")]
+impl ExactSizeIterator for EscapeUnicode { }
+
 /// An iterator that yields the literal escape code of a `char`.
 ///
 /// This `struct` is created by the [`escape_default()`] method on [`char`]. See
@@ -578,6 +581,9 @@ impl Iterator for EscapeDefault {
     }
 }
 
+#[stable(feature = "exact_size_escape", since = "1.11.0")]
+impl ExactSizeIterator for EscapeDefault { }
+
 /// An iterator over `u8` entries represending the UTF-8 encoding of a `char`
 /// value.
 ///