pretty-pretty extremal constants!

While many programmers may intuitively appreciate the significance of
"magic numbers" like −2147483648, Rust is about empowering everyone to
build reliable and efficient software! It's a bit more legible to
print the constant names (even noisy fully-qualified-paths thereof).

The bit-manipulation methods mirror those in
`librustc_mir::hair::pattern::_match::all_constructors`; thanks to the
immortal Varkor for guidance.

Resolves #56393.

src/test/ui/refutable-pattern-errors.rs

@@ -3,5 +3,5 @@ fn func((1, (Some(1), 2..=3)): (isize, (Option<isize>, isize))) { }
 
 fn main() {
     let (1, (Some(1), 2..=3)) = (1, (None, 2));
-    //~^ ERROR refutable pattern in local binding: `(-2147483648i32..=0i32, _)` not covered
+    //~^ ERROR refutable pattern in local binding: `(std::i32::MIN..=0i32, _)` not covered
 }