Generic PRAGMA URI parameters

Other drivers, in particular modernc and ncruces support a generic _pragma URI parameter.

Basically, potentially multiple PRAGMA statements are executed in the order specified in the URI for every connection opened.

Example:

sql.Open("sqlite3", "file:demo.db?_pragma=busy_timeout(10000)&_pragma=foreign_keys(on)")

This leads to the following SQL being executed:

PRAGMA busy_timeout(10000);
PRAGMA foreing_keys(on);

The values of the _pragma params are reproduced literally after URL decoding. Using the parenthesis form of PRAGMA is just a convenience for readability (_pragma=busy_timeout%3D10000 would be just as valid).

These would serve the same purpose as many of the custom parameters this driver specifies (like _fk), but would be more portable across drivers, allowing libraries like GORM, goqite or redka to be driver agnostic and customize their connections in a driver agnostic way.

Start by tracing how this driver parses URI query parameters and opens each SQLite connection. Check existing custom parameters such as _fk and the connection initialization path; done means repeated _pragma values are URL-decoded and executed in URI order for every opened connection, with coverage for the example.