Change MSVC 19.50 support for P2290 from full to partial

Signed-off-by: Cem Dervis <cem@dervis.de>

Author: cdervis

features_cpp23.yaml

@@ -205,8 +205,11 @@ features:
     support:
       - GCC 13
       - Clang 15
-      - MSVC 19.50
+      - MSVC 19.50 (partial)
       - Xcode 15
+    hints:
+      - target: MSVC 19.50
+        msg: "Only supports octal and hexadecimal escape sequences, no universal character name escape sequences."
 
   - desc: "Named universal character escapes"
     paper: P2071