This CL make bitmap_count, bitmap_union, and bitmap_union_count accept any expression whose return type is bitmap as input so that we can support flexible bitmap expression such as bitmap_count(bitmap_and(to_bitmap(1), to_bitmap(2))).
This CL also create separate documentation for each bitmap UDF to conform with other functions.
Some use has the requirment that only some of columns will be update in
one load operation, and others will retain as original. However, Doris
can't handle this situation, because user must specify value for all
columns. Then if a column aggregation method is REPLACE, use must query
original value to overwrite it. This often needs some work for user to
do.
If this CL is applied, user can use REPLACE_IF_NOT_NULL instead of
REPLACE. Then when load data to table, if user don't intent to change
value of this column, user can specify NULL for this column. Doris will
retain original value for this column.
Add a new type: Object. Currently, it's mainly for complex aggregate metrics(HLL , Bitmap).
The Object type has the following constraints：
1 Object type could not as key column type
2 Object type doesn't support all indices (BloomFilter, short key, zone map, invert index)
3 Object type doesn't support filter and group by
In the implementation：
The Object type reuse the StringValue and StringVal, because in storage engine, the Object type is binary, it has a pointer and length.
