vim-patch:9.0.0816: CTRL-Z at end of file is always dropped

Problem:    CTRL-Z at end of file is always dropped.
Solution:   Add the 'endoffile' option, like the 'endofline' option.
            (closes vim/vim#11408, closes vim/vim#11397)

Cherry-pick test_fixeol.vim changes from patch 8.2.1432.
Cherry-pick 'endoffile' changes from latest Vim runtime update.

fb0cf2357e

vim-patch:f0b567e32a46

Revert unintended Makefile change

f0b567e32a

vim-patch:72c8e3c070b3

Fix wrong struct access for member.

72c8e3c070

vim-patch:3f68a4136eb9

Add missing entry for the 'endoffile' option.

3f68a4136e

Co-authored-by: Bram Moolenaar <Bram@vim.org>

src/nvim/option_defs.h

@@ -497,6 +497,7 @@ EXTERN char_u *p_ef;            // 'errorfile'
 EXTERN char *p_efm;             // 'errorformat'
 EXTERN char *p_gefm;            // 'grepformat'
 EXTERN char *p_gp;              // 'grepprg'
+EXTERN int p_eof;               ///< 'endoffile'
 EXTERN int p_eol;               ///< 'endofline'
 EXTERN char *p_ei;              // 'eventignore'
 EXTERN int p_et;                ///< 'expandtab'
@@ -858,6 +859,7 @@ enum {
   BV_CFU,
   BV_DEF,
   BV_INC,
+  BV_EOF,
   BV_EOL,
   BV_FIXEOL,
   BV_EP,