Return Querier interface from WithTx when interface is emitted.

[0xstepit]

What do you want to change?

When you specify the flag: emit_interface: true in the sqlc.yaml, the Querier interface is generated. This is a great feature, however, the WithTx method returns a *Queries pointer, making the use of the interface hard:

func (q *Queries) WithTx(tx *sql.Tx) *Queries {
	return &Queries{
		db: tx,
	}
}

It would be great to return the interface when the previously mentioned flag is set to true:

func (q *Queries) WithTx(tx *sql.Tx) Querier {
	return &Queries{
		db: tx,
	}
}

Happy to create a PR for it if you like the idea.

What database engines need to be changed?

No response

What programming language backends need to be changed?

Go