vim: move linenr_T and colnr_T to pos.h

Try to cut down vim.h's size. It's keeping us from testing more things.

src/nvim/ex_eval.h

@@ -1,6 +1,8 @@
 #ifndef NVIM_EX_EVAL_H
 #define NVIM_EX_EVAL_H
 
+#include "nvim/pos.h"           // for linenr_T
+
 /*
  * A list used for saving values of "emsg_silent".  Used by ex_try() to save the
  * value of "emsg_silent" if it was non-zero.  When this is done, the CSF_SILENT