Try len_utf8 with one branch for ASCII's sake

Author: cuviper

library/core/src/char/methods.rs

@@ -1739,9 +1739,11 @@ impl EscapeDebugExtArgs {
 
 #[inline]
 const fn len_utf8(code: u32) -> usize {
-    1 + ((code >= MAX_ONE_B) as usize)
-        + ((code >= MAX_TWO_B) as usize)
-        + ((code >= MAX_THREE_B) as usize)
+    if code < MAX_ONE_B {
+        1
+    } else {
+        2 + ((code >= MAX_TWO_B) as usize) + ((code >= MAX_THREE_B) as usize)
+    }
 }
 
 /// Encodes a raw u32 value as UTF-8 into the provided byte buffer,