LibSQL: Allow expressions and column names in SELECT ... FROM

Up to now the only ``SELECT`` statement that worked was ``SELECT *
FROM <table>``. This commit allows a column list consisting of
column names and expressions in addition to ``*``. ``WHERE``
still doesn't work though.

Userland/Libraries/LibSQL/TupleDescriptor.h

@@ -36,6 +36,11 @@ struct TupleElementDescriptor {
     {
         return (sizeof(u32) + name.length()) + 2 * sizeof(u8);
     }
+
+    String to_string() const
+    {
+        return String::formatted("  name: {} type: {} order: {}", name, SQLType_name(type), Order_name(order));
+    }
 };
 
 class TupleDescriptor
@@ -84,6 +89,15 @@ public:
         return len;
     }
 
+    String to_string() const
+    {
+        Vector<String> elements;
+        for (auto& element : *this) {
+            elements.append(element.to_string());
+        }
+        return String::formatted("[\n{}\n]", String::join("\n", elements));
+    }
+
     using Vector<TupleElementDescriptor>::operator==;
 };