AK: Explicitly require Checked types to be Integral

These were already implicitly required to be integral via the usage of
the is_within_range templated function, but making them explicit should
produce nicer error messages when building, and make the IDE highlight
the incorrect usage.

AK/Checked.h

@@ -28,6 +28,7 @@
 #pragma once
 
 #include <AK/Assertions.h>
+#include <AK/Concepts.h>
 #include <AK/NumericLimits.h>
 #include <AK/StdLibExtras.h>
 
@@ -109,17 +110,17 @@ template<typename Destination, typename Source>
  return TypeBoundsChecker<Destination, Source>::is_within_range(value);
 }
 
-template<typename T>
+template<Integral T>
 class Checked {
 public:
  constexpr Checked() = default;
 
- constexpr Checked(T value)
+ explicit constexpr Checked(T value)
  : m_value(value)
  {
  }
 
- template<typename U>
+ template<Integral U>
  constexpr Checked(U value)
  {
  m_overflow = !is_within_range<T>(value);