Make bitmap_union agg column support insert into and broker load

[kangkaisen]

For #1610, make bitmap_union support insert into select and broker load

1 Add a check for select * with bitmap_union
2 Define the bitmap_union column type to varchar(0), because the bitmap real length is variable, when insert into, the bitmap real length maybe larger than origin varchar length.

Test the following case:

1

insert into bitmap_test_2 select id, id2 from bitmap_test_3;

2

insert into bitmap_test_2 select id, to_bitmap(id2) from bitmap_int;

3

INSERT INTO bitmap_test_2 (id, id2) VALUES (1000, to_bitmap(1000)), (1000, to_bitmap(2000));

[imay]

@kangkaisen
I have seen this PR.
I think you should check source column is a valid bitmap in InsertStatement like HLL here

[kangkaisen]

@kangkaisen
I have seen this PR.
I think you should check source column is a valid bitmap in InsertStatement like HLL here
@imay Update

[imay]

I think BITMAP_UNION() is OK too.

And you should add in
fe/src/main/java/org/apache/doris/planner/BrokerScanNode.java:452
fe/src/main/java/org/apache/doris/planner/StreamLoadScanNode.java:278

[kangkaisen]

Update

[imay]

If you want to unify BrokerScanNode and StreamScanNode, I think you'd better to make another class which is subclass of ScanNode. Because not all ScanNode has these properties, they only are used in loading.

[morningman]

There are a lot change related to load process in my pull request #1695 .
So...Please do not change any class name or class inheritance relationship at this time.
T.T

[kangkaisen]

There are a lot change related to load process in my pull request #1695 .
So...Please do not change any class name or class inheritance relationship at this time.
T.T

OK. I has minimized the change.

[imay]

LGTM