refactor: move some functions to winfloat.c (#26020)

src/nvim/ex_docmd.c

@@ -83,6 +83,7 @@
 #include "nvim/usercmd.h"
 #include "nvim/vim.h"
 #include "nvim/window.h"
+#include "nvim/winfloat.h"
 
 static const char e_ambiguous_use_of_user_defined_command[]
   = N_("E464: Ambiguous use of user-defined command");