Move vector into core from extensions

[krishvishal]

To make implementation of DiskANN in limbo easier, I'm moving vector from extensions to core.

Now vector related function are exposed via Function op code.

I've defined a new enum called VectorFunc to group the vector related functions.

The vector.test TCL test runs fine.

limbo>   SELECT vector_extract(vector('[]'));
[]
limbo> SELECT vector_extract(vector('  [  1  ,  2  ,  3  ]  '));
[1,2,3]
limbo> SELECT vector_extract(vector('[-1000000000000000000]'));
[-1000000000000000000]
limbo> SELECT vector_distance_cos(vector('[1,2,3]'), vector('[3,2,1]'));
0.2857142686843872