style(miscellaneous): move Placeholders.h from Templates to Miscellaneous

Redcraft.Utility/Source/Public/Miscellaneous/Placeholders.h

@@ -0,0 +1,36 @@
+#pragma once
+
+#include "CoreTypes.h"
+#include "TypeTraits/HelperClasses.h"
+
+NAMESPACE_REDCRAFT_BEGIN
+NAMESPACE_MODULE_BEGIN(Redcraft)
+NAMESPACE_MODULE_BEGIN(Utility)
+
+struct FForceInit { explicit FForceInit() = default; };
+inline constexpr FForceInit ForceInit{};
+
+struct FNoInit { explicit FNoInit() = default; };
+inline constexpr FNoInit NoInit{};
+
+struct FInvalid { explicit FInvalid() = default; };
+inline constexpr FInvalid Invalid{};
+
+struct FInPlace { explicit FInPlace() = default; };
+inline constexpr FInPlace InPlace{};
+
+template <typename T> struct TInPlaceType { explicit TInPlaceType() = default; };
+template <typename T> inline constexpr TInPlaceType<T> InPlaceType{};
+
+template <size_t I> struct TInPlaceIndex { explicit TInPlaceIndex() = default; };
+template <size_t I> inline constexpr TInPlaceIndex<I> InPlaceIndex{};
+
+template <typename T> struct TIsInPlaceTypeSpecialization                  : FFalse { };
+template <typename T> struct TIsInPlaceTypeSpecialization<TInPlaceType<T>> : FTrue  { };
+
+template <typename T> struct TIsInPlaceIndexSpecialization                   : FFalse { };
+template <size_t   I> struct TIsInPlaceIndexSpecialization<TInPlaceIndex<I>> : FTrue  { };
+
+NAMESPACE_MODULE_END(Utility)
+NAMESPACE_MODULE_END(Redcraft)
+NAMESPACE_REDCRAFT_END