refactor(options): reduce `findoption()` usage

Problem: Many places in the code use `findoption()` to access an option using its name, even if the option index is available. This is very slow because it requires looping through the options array over and over.

Solution: Use option index instead of name wherever possible. Also introduce an `OptIndex` enum which contains the index for every option as enum constants, this eliminates the need to pass static option names as strings.

1 files changed, 2 insertions, 2 deletions

diff --git a/src/nvim/fileio.c b/src/nvim/fileio.c
index 4fe5b1cd44..0e2959835b 100644
--- a/src/nvim/fileio.c
+++ b/src/nvim/fileio.c
@@ -1617,7 +1617,7 @@ failed:
     save_file_ff(curbuf);
     // If editing a new file: set 'fenc' for the current buffer.
     // Also for ":read ++edit file".
-    set_string_option_direct("fenc", -1, fenc, OPT_FREE | OPT_LOCAL, 0);
+    set_string_option_direct(kOptFileencoding, fenc, OPT_FREE | OPT_LOCAL, 0);
   }
   if (fenc_alloced) {
     xfree(fenc);
@@ -1965,7 +1965,7 @@ void set_forced_fenc(exarg_T *eap)
   }
 
   char *fenc = enc_canonize(eap->cmd + eap->force_enc);
-  set_string_option_direct("fenc", -1, fenc, OPT_FREE|OPT_LOCAL, 0);
+  set_string_option_direct(kOptFileencoding, fenc, OPT_FREE|OPT_LOCAL, 0);
   xfree(fenc);
 }