refactor(options): autogenerate valid values and flag enums for options (#31089)

Problem: Option metadata like list of valid values for an option and
option flags are not listed in the `options.lua` file and are instead
manually defined in C, which means option metadata is split between
several places.

Solution: Put metadata such as list of valid values for an option and
option flags in `options.lua`, and autogenerate the corresponding C
variables and enums.

Supersedes #28659

Co-authored-by: glepnir <glephunter@gmail.com>

src/nvim/buffer_defs.h

@@ -316,8 +316,6 @@ typedef struct {
   char *b_p_spf;              // 'spellfile'
   char *b_p_spl;              // 'spelllang'
   char *b_p_spo;              // 'spelloptions'
-#define SPO_CAMEL  0x1
-#define SPO_NPBUFFER 0x2
   unsigned b_p_spo_flags;      // 'spelloptions' flags
   int b_cjk;                  // all CJK letters as OK
   uint8_t b_syn_chartab[32];  // syntax iskeyword option