The following PR addresses aims to remove the warnings from sphinx that are raised for xml.sax.rst. (total 3 warnings)

Warnings removed:

WARNING: py:class reference target not found: xml.sax.xmlreader.Attributes [ref.class]
WARNING: py:class reference target not found: xml.sax.xmlreader.AttributesNS [ref.class]

• The above warnings were removed by replacing xml.sax.xmlreader.Attributes with xml.sax.xmlreader.AttributesImpl and
  xml.sax.xmlreader.AttributesNS with xml.sax.xmlreader.AttributesNSImpl.

Verification :

• for xml.sax.xmlreader.AttributesImpl : xml.sax.reader.rst
• for xml.sax.xmlreader.AttributesNSImpl: xml.sax.reader.rst

Warnings remaining:

WARNING: py:func reference target not found: create_parser [ref.func]

• The above warning is due to the absence of documentation for create_parser function. We can either add documentation for it or remove the documentation's reference to create_parser. Waiting for suggestions.

• Issue: Fix all Sphinx reference warnings in Doc/library/{xml*,pyexpat}.rst #151943