sql: pg_function_is_visible is not correct for UDFs

[rafiss]

Describe the problem

This builtin was added in 2019. The assumptions from back then no longer hold. See:

cockroach/pkg/sql/sem/builtins/pg_builtins.go

Lines 1178 to 1195 in 1ca61ae

	// pg_function_is_visible returns true if the input oid corresponds to a
	// builtin function that is part of the databases on the search path.
	// CockroachDB doesn't have a concept of namespaced functions, so this is
	// always true if the builtin exists at all, and NULL otherwise.
	// https://www.postgresql.org/docs/9.6/static/functions-info.html
	"pg_function_is_visible": makeBuiltin(defProps(),
	tree.Overload{
	Types: tree.ArgTypes{{"oid", types.Oid}},
	ReturnType: tree.FixedReturnType(types.Bool),
	Fn: func(ctx *eval.Context, args tree.Datums) (tree.Datum, error) {
	oid := tree.MustBeDOid(args[0])
	t, err := ctx.Planner.QueryRowEx(
	ctx.Ctx(), "pg_function_is_visible",
	sessiondata.NoSessionDataOverride,
	"SELECT * from pg_proc WHERE oid=$1 LIMIT 1", oid.Oid)
	if err != nil {
	return nil, err
	}

Expected behavior
Match the Postgres implementation, and take into account the schemas on the search path. Maybe it also takes into account privileges?

Also, the current implementation is needlessly slow. I hope we can improve the speed of it too.

Environment:

• CockroachDB v22.2.0-beta

cc @chengxiong-ruan @mgartner

Jira issue: CRDB-20297

Epic CRDB-19147

[rafiss]

The fix here is going to be every similar to what I did in #90649 so I can take this issue.