xml: Add missing types for DocumentType's publicId and systemId

[JPTIZ]

Remarks:

1. I've looked through the actual implementation and the usage of str | None should make sense. For the None part, the stdlib implementation use a few if obj.publicId:, see for example:

   $ grep -n -R publicId  /usr/lib/python3.12/xml/dom/
   /usr/lib/python3.12/xml/dom/xmlbuilder.py:215:    def resolveEntity(self, publicId, systemId):
   /usr/lib/python3.12/xml/dom/xmlbuilder.py:218:        source.publicId = publicId
   /usr/lib/python3.12/xml/dom/xmlbuilder.py:258:                 'encoding', 'publicId', 'systemId', 'baseURI')
   /usr/lib/python3.12/xml/dom/xmlbuilder.py:265:        self.publicId = None
   /usr/lib/python3.12/xml/dom/xmlbuilder.py:289:    def _get_publicId(self):
   /usr/lib/python3.12/xml/dom/xmlbuilder.py:290:        return self.publicId
   /usr/lib/python3.12/xml/dom/xmlbuilder.py:291:    def _set_publicId(self, publicId):
   /usr/lib/python3.12/xml/dom/xmlbuilder.py:292:        self.publicId = publicId
   /usr/lib/python3.12/xml/dom/minidom.py:1294:    """Mix-in class that supports the publicId and systemId attributes."""
   /usr/lib/python3.12/xml/dom/minidom.py:1296:    __slots__ = 'publicId', 'systemId'
   /usr/lib/python3.12/xml/dom/minidom.py:1298:    def _identified_mixin_init(self, publicId, systemId):
   /usr/lib/python3.12/xml/dom/minidom.py:1299:        self.publicId = publicId
   /usr/lib/python3.12/xml/dom/minidom.py:1302:    def _get_publicId(self):
   /usr/lib/python3.12/xml/dom/minidom.py:1303:        return self.publicId
   /usr/lib/python3.12/xml/dom/minidom.py:1312:    publicId = None
   /usr/lib/python3.12/xml/dom/minidom.py:1338:                    notation = Notation(n.nodeName, n.publicId, n.systemId)
   /usr/lib/python3.12/xml/dom/minidom.py:1342:                    entity = Entity(e.nodeName, e.publicId, e.systemId,
   /usr/lib/python3.12/xml/dom/minidom.py:1357:        if self.publicId:
   /usr/lib/python3.12/xml/dom/minidom.py:1359:                         % (newl, self.publicId, newl, self.systemId))
   /usr/lib/python3.12/xml/dom/minidom.py:1377:    def __init__(self, name, publicId, systemId, notation):
   /usr/lib/python3.12/xml/dom/minidom.py:1381:        self._identified_mixin_init(publicId, systemId)
   /usr/lib/python3.12/xml/dom/minidom.py:1412:    def __init__(self, name, publicId, systemId):
   /usr/lib/python3.12/xml/dom/minidom.py:1414:        self._identified_mixin_init(publicId, systemId)
   /usr/lib/python3.12/xml/dom/minidom.py:1478:    def createDocumentType(self, qualifiedName, publicId, systemId):
   /usr/lib/python3.12/xml/dom/minidom.py:1480:        doctype.publicId = publicId
   /usr/lib/python3.12/xml/dom/minidom.py:1731:    def _create_entity(self, name, publicId, systemId, notationName):
   /usr/lib/python3.12/xml/dom/minidom.py:1732:        e = Entity(name, publicId, systemId, notationName)
   /usr/lib/python3.12/xml/dom/minidom.py:1736:    def _create_notation(self, name, publicId, systemId):
   /usr/lib/python3.12/xml/dom/minidom.py:1737:        n = Notation(name, publicId, systemId)
   /usr/lib/python3.12/xml/dom/minidom.py:1936:            node.name, node.publicId, node.systemId)
   /usr/lib/python3.12/xml/dom/minidom.py:1942:                notation = Notation(n.nodeName, n.publicId, n.systemId)
   /usr/lib/python3.12/xml/dom/minidom.py:1948:                entity = Entity(e.nodeName, e.publicId, e.systemId,
   /usr/lib/python3.12/xml/dom/expatbuilder.py:237:    def start_doctype_decl_handler(self, doctypeName, systemId, publicId,
   /usr/lib/python3.12/xml/dom/expatbuilder.py:240:            doctypeName, publicId, systemId)
   /usr/lib/python3.12/xml/dom/expatbuilder.py:303:                            base, systemId, publicId, notationName):
   /usr/lib/python3.12/xml/dom/expatbuilder.py:309:        node = self.document._create_entity(entityName, publicId,
   /usr/lib/python3.12/xml/dom/expatbuilder.py:320:    def notation_decl_handler(self, notationName, base, systemId, publicId):
   /usr/lib/python3.12/xml/dom/expatbuilder.py:321:        node = self.document._create_notation(notationName, publicId, systemId)
   /usr/lib/python3.12/xml/dom/expatbuilder.py:340:    def external_entity_ref_handler(self, context, base, systemId, publicId):
   /usr/lib/python3.12/xml/dom/expatbuilder.py:627:            if doctype.publicId:
   /usr/lib/python3.12/xml/dom/expatbuilder.py:629:                         % (doctype.publicId, doctype.systemId))
   /usr/lib/python3.12/xml/dom/expatbuilder.py:660:                if notation.publicId:
   /usr/lib/python3.12/xml/dom/expatbuilder.py:662:                        % (s, notation.publicId, notation.systemId)
   /usr/lib/python3.12/xml/dom/expatbuilder.py:670:                if entity.publicId:
   /usr/lib/python3.12/xml/dom/expatbuilder.py:672:                        % (s, entity.publicId, entity.systemId)
   /usr/lib/python3.12/xml/dom/expatbuilder.py:685:    def external_entity_ref_handler(self, context, base, systemId, publicId):
   /usr/lib/python3.12/xml/dom/expatbuilder.py:705:                self, context, base, systemId, publicId)
   /usr/lib/python3.12/xml/dom/expatbuilder.py:877:    def start_doctype_decl_handler(self, name, publicId, systemId,

2. The str | None types can also be infered from DocumentType docs
3. The DomImplementation.createDocumentType method in stdlib implementation does a straight-forward assignment:

       def createDocumentType(self, qualifiedName, publicId, systemId):
           doctype = DocumentType(qualifiedName)
           doctype.publicId = publicId
           doctype.systemId = systemId
           return doctype

   So, changing the publicId and systemId parameter types to str | None should make sense as well.

[github-actions]

According to mypy_primer, this change has no effect on the checked open source code. 🤖🎉

[tungol]

I pushed up a bigger xml MR within 24 hours of this one, funny enough. I just checked and I came to the same conclusion in both of these places in #13349, so +1 from me here.

[srittau]

Thanks!