bpo-33497: Add errors param to cgi.parse_multipart and make an encoding in FieldStorage use the given errors (GH-6804) (GH-6837)

(cherry picked from commit 545c955be997efd6b3827b981024e6b9945d82d1)

Co-authored-by: Amber Brown <hawkowl@atleastfornow.net>
diff --git a/Doc/library/cgi.rst b/Doc/library/cgi.rst
index 17386b8..0b1aead 100644
--- a/Doc/library/cgi.rst
+++ b/Doc/library/cgi.rst
@@ -296,7 +296,7 @@
    instead. It is maintained here only for backward compatibility.
 
 
-.. function:: parse_multipart(fp, pdict, encoding="utf-8")
+.. function:: parse_multipart(fp, pdict, encoding="utf-8", errors="replace")
 
    Parse input of type :mimetype:`multipart/form-data` (for  file uploads).
    Arguments are *fp* for the input file, *pdict* for a dictionary containing
@@ -312,8 +312,8 @@
    which is much more flexible.
 
    .. versionchanged:: 3.7
-      Added the *encoding* parameter.  For non-file fields, the value is now
-      a list of strings, not bytes.
+      Added the *encoding* and *errors* parameters.  For non-file fields, the
+      value is now a list of strings, not bytes.
 
 
 .. function:: parse_header(string)