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/main.c

@@ -628,7 +628,7 @@ int main(int argc, char **argv)
   }
 
   // WORKAROUND(mhi): #3023
-  if (cb_flags & CB_UNNAMEDMASK) {
+  if (cb_flags & (kOptCbFlagUnnamed | kOptCbFlagUnnamedplus)) {
     eval_has_provider("clipboard", false);
   }