Prevent ALTER TYPE/DOMAIN/OPERATOR from changing extension membership.

If recordDependencyOnCurrentExtension is invoked on a pre-existing,
free-standing object during an extension update script, that object
will become owned by the extension.  In our current code this is
possible in three cases:

* Replacing a "shell" type or operator.
* CREATE OR REPLACE overwriting an existing object.
* ALTER TYPE SET, ALTER DOMAIN SET, and ALTER OPERATOR SET.

The first of these cases is intentional behavior, as noted by the
existing comments for GenerateTypeDependencies.  It seems like
appropriate behavior for CREATE OR REPLACE too; at least, the obvious
alternatives are not better.  However, the fact that it happens during
ALTER is an artifact of trying to share code (GenerateTypeDependencies
and makeOperatorDependencies) between the CREATE and ALTER cases.
Since an extension script would be unlikely to ALTER an object that
didn't already belong to the extension, this behavior is not very
troubling for the direct target object ... but ALTER TYPE SET will
recurse to dependent domains, and it is very uncool for those to
become owned by the extension if they were not already.

Let's fix this by redefining the ALTER cases to never change extension
membership, full stop.  We could minimize the behavioral change by
only changing the behavior when ALTER TYPE SET is recursing to a
domain, but that would complicate the code and it does not seem like
a better definition.

Per bug #17144 from Alex Kozhemyakin.  Back-patch to v13 where ALTER
TYPE SET was added.  (The other cases are older, but since they only
affect the directly-named object, there's not enough of a problem to
justify changing the behavior further back.)

Discussion: https://postgr.es/m/17144-e67d7a8f049de9af@postgresql.org

src/backend/catalog/pg_depend.c

@@ -179,6 +179,13 @@ recordMultipleDependencies(const ObjectAddress *depender,
  * existed), so we must check for a pre-existing extension membership entry.
  * Passing false is a guarantee that the object is newly created, and so
  * could not already be a member of any extension.
+ *
+ * Note: isReplace = true is typically used when updating a object in
+ * CREATE OR REPLACE and similar commands.  The net effect is that if an
+ * extension script uses such a command on a pre-existing free-standing
+ * object, the object will be absorbed into the extension.  If the object
+ * is already a member of some other extension, the command will fail.
+ * This behavior is desirable for cases such as replacing a shell type.
  */
 void
 recordDependencyOnCurrentExtension(const ObjectAddress *object,