This PR addresses the points raised in #9262 by doing the following:

Updating magic method exception messages

Previously the error message:

Enum may not include magic method %s

Was only used for:

• __sleep
• __wakeup
• __set_state

All of which I believe are "technically" not magic methods, whereas all of the other true magic methods gave the error message:

Enum may not include %s

This PR updates it so that all true magic methods also give the following error:

Enum may not include magic method %s

Normalising double quote usage in error messages

Enum error messages were inconsistent in their usage of double quotes with an enum name, as well as with values.

This PR changes the following error messages:

Properties

Enum "%s" may not include properties

Is now

Enum %s may not include properties

Backing

"%s" is not a valid backing value for enum "%s"

Is now

"%s" is not a valid backing value for enum %s

In the spirit of keeping this consistent, double quotes have been added to the value when the backing type is int.

Added missing tests

I've also added tests for all of the magic methods that weren't previously covered.

Stringable

Nothing was done with the Stringable interface, as originally planned, because the usage of __toString was always caught before the interface.