Rollup merge of rust-lang#81409 - gilescope:chars_count, r=joshtriplett

Slight simplification of chars().count()

Slight simplification: No need to call len(), we can just count the number of non continuation bytes.

I can't see any reason not to do this, can you?

library/core/src/str/iter.rs

@@ -47,12 +47,7 @@ impl<'a> Iterator for Chars<'a> {
     #[inline]
     fn count(self) -> usize {
         // length in `char` is equal to the number of non-continuation bytes
-        let bytes_len = self.iter.len();
-        let mut cont_bytes = 0;
-        for &byte in self.iter {
-            cont_bytes += utf8_is_cont_byte(byte) as usize;
-        }
-        bytes_len - cont_bytes
+        self.iter.filter(|&&byte| !utf8_is_cont_byte(byte)).count()
     }
 
     #[inline]