Expose type modifier in Column struct

[SergeiPatiakin]

What

Expose the 4-byte type-specific type modifier on the Column struct

Why

I would like access type modifiers for prepared statement columns. E.g. for a numeric column I would like to get the numeric precision and scale. For a varchar column I would like to get the varchar length limit.

Context

This is an extension of #1084 where other table and column OIDs were exposed in Column, and exposing type modifiers was noted as a possibility.

[rishitesh-snt]

+1 for this PR. This would enable the result set handling in a much better way rather than falling back to defaults. In fact, rather than type modifier, we should expose the derived precision & scale at the upper level API like Statement.