refactor(tui): use nvim_echo() for verbose terminfo

This is needed for #18375 for the obvious reasons.
note: verbose_terminfo_event is only temporarily needed
until the full TUI process refactor is merged.

src/nvim/charset.h

@@ -7,6 +7,7 @@
 #include "nvim/eval/typval.h"
 #include "nvim/option_defs.h"
 #include "nvim/pos.h"
+#include "nvim/strings.h"
 #include "nvim/types.h"
 
 /// Return the folded-case equivalent of the given character