Add collect agg function

[acquamarin]

This PR adds support for collect function.

LIST agg function:

1. Description:

Returns a LIST containing all the values of a column.

2. Example:

MATCH (p:person) RETURN p.gender, collect(p.workedHours)
1|[[10,5],[4,5],[2]]
2|[[12,8],[1,9],[3,4,5,6,7],[1],[10,11,12,3,4,5,6,7]]

3. Implementation:

a. The aggregate operator will accumulate elements in a factorizedTable which is stored in the collectAggState.
b. During the AggregateScan: the collectAggState will output all the elements as a list and store the list in the output valueVector.

4. Note:

a. We currently do not support compute hash value for ku_list_t. Therefore, users are not allowed to run a query which requires to compute the hash value of ku_list_t.
E.g.

MATCH (p:person) RETURN collect(distinct p.workedHours)

This query needs to compute the hash value of p.workedHours, which is not supported.

b. We currently do not support storing NULL values in ku_list_t. If the elements to collect contain NULL, undefined behaviour may happen during query processing.

[andyfengHKU]

Overall looks fine to me. But @ray6080 should take a look

[ray6080]

Let's get this in. Once we're done with changes in buffer manager, we can revisit these designs again.