LibSQL: Move Order and Nulls enums from SQL::AST to SQL namespace

The Order enum is used in the Meta component of LibSQL. Using this enum
meant having to include the monster AST/AST.h include file. Furthermore,
they are sort of basic and therefore can live in the general SQL
namespace. Moved to LibSQL/Type.h.

Also introduced a new class, SQLResult, which is needed in future
patches.

Userland/Libraries/LibSQL/AST/AST.h

@@ -13,6 +13,8 @@
 #include <AK/String.h>
 #include <LibSQL/AST/Token.h>
 #include <LibSQL/Forward.h>
+#include <LibSQL/SQLResult.h>
+#include <LibSQL/Type.h>
 
 namespace SQL::AST {
 
@@ -251,16 +253,6 @@ private:
     NonnullRefPtrVector<TableOrSubquery> m_subqueries {};
 };
 
-enum class Order {
-    Ascending,
-    Descending,
-};
-
-enum class Nulls {
-    First,
-    Last,
-};
-
 class OrderingTerm : public ASTNode {
 public:
     OrderingTerm(NonnullRefPtr<Expression> expression, String collation_name, Order order, Nulls nulls)