Add pre-defined vector types

[taichi-ishitani]

close #1029

[dalance]

Actual usage seems to be like below.
I think it is redundant, and types package may be sufficient.

var a: $std::std_types_pkg::il32;

var a: $std::types::il32;

[taichi-ishitani]

Actual usage seems to be like below. I think it is redundant, and types package may be sufficient.

var a: $std::std_types_pkg::il32;

var a: $std::types::il32;

I changed the package name.