fix(messages): typo and unwanted truncation in msg_outtrans_long #31669

- Typo/bug in msg_outtrans_long passing string length as "hist" argument.
- Avoid truncating message in msg_outtrans_long with ext_messages (followup to 
  1097d239c3).
- Remove `_hl` from `msg_keep`, `smsg_keep` as there is no non-`_hl` variant.
- `msg_printf_hl` is removed (identical to `smsg` except it sets
  `msg_scroll = true`, seemingly as a caveat to force a more prompt in
  cmdline mode). Move this logic to the only the only place this was
  used in ex_getln.c.

src/nvim/ex_getln.c

@@ -3142,8 +3142,9 @@ static bool color_cmdline(CmdlineInfo *colored_ccline)
 
 #define PRINT_ERRMSG(...) \
   do { \
+    msg_scroll = true; \
     msg_putchar('\n'); \
-    msg_printf_hl(HLF_E, __VA_ARGS__); \
+    smsg(HLF_E, __VA_ARGS__); \
     printed_errmsg = true; \
   } while (0)
   bool ret = true;