[Pg] Handle geometry types

[brncsk]

This is a reopen of #2803 targeted against the beta branch.

Fixes #2675 (includes something like #2774), but also adds support for geometry types (e.g. MultiPolygon, LineString etc.)

NOTES:

• It's a preliminary version as [Pg] Schema support for PostGIS geometry types & SRIDs #2803 was, but I'm still willing to bring it up to production quality.
• I'm also unsure about whether or not supporting lowercase geometry types (e.g. point) is a good thing, see You're about to change geom column type from geometry(Point) to geometry(point) messages when running drizzle-kit push.
• It does not include support for mapping from/to driver values (e.g. [Pg] Add PostGIS MultiLineString support #2769) ATM