use full unicode mappings for upper/lower/title case (#12736)

Also broaden the category of characters that count as lowercase/uppercase.
diff --git a/Misc/NEWS b/Misc/NEWS
index 77b232d..4cfccae 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -10,6 +10,8 @@
 Core and Builtins
 -----------------
 
+- Issue #12736: Use full unicode case mappings for upper, lower, and title case.
+
 - Issue #12760: Add a create mode to open(). Patch by David Townshend.
 
 - Issue #13738: Simplify implementation of bytes.lower() and bytes.upper().