[3.9] bpo-45461: Fix IncrementalDecoder and StreamReader in the "unicode-escape"...

[3.9] bpo-45461: Fix IncrementalDecoder and StreamReader in the "unicode-escape" codec (GH-28939) (GH-28945)

They support now splitting escape sequences between input chunks.

Add the third parameter "final" in codecs.unicode_escape_decode().
It is True by default to match the former behavior.
(cherry picked from commit c96d1546b11b4c282a7e21737cb1f5d16349656d)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
Origin: backport, https://github.com/python/cpython/commit/7c722e32bf582108680f49983cf01eaed710ddb9

Gbp-Pq: Name CVE-2025-4516-1.patch