untrusted PLs should be GRANTable

A user has raised the point that our refusal to GRANT rights to untrusted PLs is counterproductive and inconsistent with how we behave elsewhere.

Yes, untrusted PLs can be escaped to gain superuser rights, often trivially.

But we allow this:

CREATE ROLE superme SUPERUSER NOINHERIT;

GRANT superme TO me;

.... and really, GRANTing an untrusted PL is similar.

Forcing users to create their PLs as a superuser increases the routine use of superuser accounts. Most users' DDL deploy scripts will get be run as a superuser if they have to use a superuser for PL changes; they're not going to SET ROLE and RESET ROLE around the function changes.

It also encourages users to make their untrusted functions SECURITY DEFINER when still owned by a superuser, which we really don't want them doing unnecessarily.

In the name of making things more secure, we've made them less secure.

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