Missing [NO] INDENT flag in XMLSerialize backward parsing

Hi,

This patch adds the missing [NO] INDENT flag to XMLSerialize backward
parsing. For example:

CREATE VIEW v1 AS
SELECT
  xmlserialize(
    DOCUMENT '<foo><bar>42</bar></foo>'::xml AS text
    INDENT);

\sv v1
CREATE OR REPLACE VIEW public.v1 AS
 SELECT XMLSERIALIZE(DOCUMENT '<foo><bar>42</bar></foo>'::xml AS
 text INDENT) AS "xmlserialize"

SELECT * FROM v1;
  xmlserialize
-----------------
 <foo>          +
   <bar>42</bar>+
 </foo>
(1 row)

The NO INDENT flag is added by default if no explicit indentation
flag was originally provided:

CREATE VIEW v2 AS
SELECT
  xmlserialize(
    DOCUMENT '<foo><bar>42</bar></foo>'::xml AS text
    NO INDENT);

\sv v2
CREATE OR REPLACE VIEW public.v2 AS
 SELECT XMLSERIALIZE(DOCUMENT '<foo><bar>42</bar></foo>'::xml AS text NO
INDENT) AS "xmlserialize"

CREATE VIEW v3 AS
SELECT
  xmlserialize(
    DOCUMENT '<foo><bar>42</bar></foo>'::xml AS text);

\sv v3
CREATE OR REPLACE VIEW public.v3 AS
 SELECT XMLSERIALIZE(DOCUMENT '<foo><bar>42</bar></foo>'::xml AS text NO
INDENT) AS "xmlserialize"

Regression tests were updated accordingly.

Best regards, Jim