LibSQL: Parse and execute sequential placeholder values

This partially implements SQLite's bind-parameter expression to support
indicating placeholder values in a SQL statement. For example:

    INSERT INTO table VALUES (42, ?);

In the above statement, the '?' identifier is a placeholder. This will
allow clients to compile statements a single time while running those
statements any number of times with different placeholder values.

Further, this will help mitigate SQL injection attacks.

Userland/Libraries/LibSQL/AST/Parser.cpp

@@ -401,7 +401,6 @@ NonnullRefPtr<Expression> Parser::parse_expression()
     if (match_secondary_expression())
         expression = parse_secondary_expression(move(expression));
 
-    // FIXME: Parse 'bind-parameter'.
     // FIXME: Parse 'function-name'.
     // FIXME: Parse 'raise-function'.
 
@@ -414,6 +413,9 @@ NonnullRefPtr<Expression> Parser::parse_primary_expression()
     if (auto expression = parse_literal_value_expression())
         return expression.release_nonnull();
 
+    if (auto expression = parse_bind_parameter_expression())
+        return expression.release_nonnull();
+
     if (auto expression = parse_column_name_expression())
         return expression.release_nonnull();
 
@@ -528,6 +530,21 @@ RefPtr<Expression> Parser::parse_literal_value_expression()
     return {};
 }
 
+// https://sqlite.org/lang_expr.html#varparam
+RefPtr<Expression> Parser::parse_bind_parameter_expression()
+{
+    // FIXME: Support ?NNN, :AAAA, @AAAA, and $AAAA forms.
+    if (consume_if(TokenType::Placeholder)) {
+        auto parameter = m_parser_state.m_bound_parameters;
+        if (++m_parser_state.m_bound_parameters > Limits::maximum_bound_parameters)
+            syntax_error(DeprecatedString::formatted("Exceeded maximum number of bound parameters {}", Limits::maximum_bound_parameters));
+
+        return create_ast_node<Placeholder>(parameter);
+    }
+
+    return {};
+}
+
 RefPtr<Expression> Parser::parse_column_name_expression(DeprecatedString with_parsed_identifier, bool with_parsed_period)
 {
     if (with_parsed_identifier.is_null() && !match(TokenType::Identifier))