Support plpgsql multi-range in conditional control

Dear hackers, my good friend Hou Jiaxing and I have implemented a version of the code that supports multiple integer range conditions in the in condition control of the for loop statement in the plpgsql procedural language. A typical example is as follows:

postgres=# do $$
declare
i int := 10;
begin
for i in 1..10 by 3, reverse i+10..i+1 by 3 loop
raise info '%', i;
end loop;
end $$;
INFO: 1
INFO: 4
INFO: 7
INFO: 10
INFO: 20
INFO: 17
INFO: 14
INFO: 11
do
postgres=#

Hope to get your feedback, thank you!

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