fix swap of e.g .eastl::list<unique_ptr[]> with stateless/default allocator

...or any other type that has deleted copy ctor.
Assume that if `allocator_type` is empty (*) then it's automatically
equal to passed instance and we can erase compile-time const assignment
branch, which is not compiles when T's copy ctor is deleted (e.g. unique_ptr)

(*) implicitly implied EASTL_NAME_ENABLED being off, since it's makes
allocator_type statefull

Author: Vladimir 'virtul' Ivannikov

include/EASTL/list.h

@@ -1571,12 +1571,14 @@ namespace eastl
 	template <typename T, typename Allocator>
 	inline void list<T, Allocator>::swap(this_type& x)
 	{
-		if(internalAllocator() == x.internalAllocator()) // If allocators are equivalent...
+		if constexpr (is_empty_v<allocator_type>)
+			DoSwap(x);
+		else if (internalAllocator() == x.internalAllocator()) // If allocators are equivalent...
 			DoSwap(x);
 		else // else swap the contents.
 		{
-			const this_type temp(*this); // Can't call eastl::swap because that would
-			*this = x;                   // itself call this member swap function.
+			this_type temp(*this); // Can't call eastl::swap because that would
+			*this = x;             // itself call this member swap function.
 			x     = temp;
 		}
 	}