make Base.uabs public 2 (#53503)

`Base.uabs` is helpful when writing code that works with generic
integers without worrying about silent overflows or overflow errors when
using integers from
[SaferIntegers.jl](https://github.com/JeffreySarnoff/SaferIntegers.jl)

`Base.uabs` is already being used by a few packages
https://juliahub.com/ui/Search?q=uabs&type=code&w=true and has a
docstring. However, it is currently an internal function.

Ref: JeffreySarnoff/SaferIntegers.jl#41

Copy of #53376

Author: nhz2

base/float.jl

@@ -224,7 +224,7 @@ function ieee754_representation(
 end
 
 """
-    uabs(x::Integer)
+    Base.uabs(x::Integer)
 
 Return the absolute value of `x`, possibly returning a different type should the
 operation be susceptible to overflow. This typically arises when `x` is a two's complement

base/public.jl

@@ -80,6 +80,9 @@ public
     isoperator,
     isunaryoperator,
 
+# scalar math
+    uabs,
+
 # C interface
     cconvert,
     unsafe_convert,

doc/src/base/math.md

@@ -187,6 +187,7 @@ Base.invmod
 Base.powermod
 Base.ndigits
 Base.add_sum
+Base.uabs
 Base.widemul
 Base.Math.evalpoly
 Base.Math.@evalpoly