enhancement: Split out ST_SetSRID string implementation into ST_SetCRS and add ST_CRS

[jesspav]

Currently we have an implementation for ST_SetSRID that allows for a CRS string. Breaking it out into ST_SetCRS (string) and ST_SetSRID (int) to align ST_SetSRID with external implementations and so that we can pass the results of ST_CRS into transforms, etc. Also need an implementation for ST_SetCrs.

Requirements:

• ST_SetSRID split into new ST_SetSRID and ST_SetCRS
• ST_CRS is impemented
• integration tests for both (although only ST_SetSRID will run against PostGIS)
• bench marks for all three

[paleolimbot]

Closed in #37 and #38!