Handle DOUBLE PRECISION data type in the backend.

[kgodey]

This issue is to ensure that Mathesar can handle the Postgres DOUBLE PRECISION data type.

As part of this issue, we need to ensure that:

• Users can use the API to change a column to DOUBLE PRECISION if it's possible to do so.
• There's nothing to do here on automatic type inference. It should never suggest DOUBLE PRECISION since we're aiming to be friendly to non-technical users and floating points can be confusing.

Additional Context

• See PR Extend the v0/databases/'s types list to show both Mathesar and DB type information. #368 for code that calculates which types are allowed for a column.