Change bit_width(T) to return int rather than T.

This matches std::bit_width().

Bug: chromium:1292951
PiperOrigin-RevId: 468495319
Change-Id: I0e428addb6a7353abbf2063c5c2f5820c3bae789

absl/numeric/bits.h

@@ -131,10 +131,9 @@ has_single_bit(T x) noexcept {
 // fractional part discarded.
 template <class T>
 ABSL_INTERNAL_CONSTEXPR_CLZ inline
-    typename std::enable_if<std::is_unsigned<T>::value, T>::type
+    typename std::enable_if<std::is_unsigned<T>::value, int>::type
     bit_width(T x) noexcept {
-  return std::numeric_limits<T>::digits -
-         static_cast<unsigned int>(countl_zero(x));
+  return std::numeric_limits<T>::digits - countl_zero(x);
 }
 
 // Returns: If x == 0, 0; otherwise the maximal value y such that