Closes: #2323
This PR adds support for two new vector functions:
* vector_concat(x, y) – Concatenates two vectors of the same type.
* vector_slice(x, start_index, end_index) – Extracts a subvector from
the input vector.
Notes:
* Negative start_index or end_index is not supported
Reviewed-by: Nikita Sivukhin (@sivukhin)
Closes#2336