feat(defaults): limit syntax cost on CmdwinEnter #15401

Add a new default autocommand to limit syntax highlighting
synchronization in the command window. This refactors the nvim_terminal
autocommand out of main() and into a new init_default_autocmds()
function, which is now part of the startup process and can be further
extended with more default autocommands down the road.

ref #6289 #6399

src/nvim/main.c

@@ -309,9 +309,6 @@ int main(int argc, char **argv)
   init_highlight(true, false);  // Default highlight groups.
   TIME_MSG("init highlight");
 
-  init_default_mappings();  // Default mappings.
-  TIME_MSG("init default mappings");
-
   // Set the break level after the terminal is initialized.
   debug_break_level = params.use_debug_break_level;
 
@@ -340,21 +337,11 @@ int main(int argc, char **argv)
     TIME_MSG("initialized screen early for UI");
   }
 
-  // open terminals when opening files that start with term://
-#define PROTO "term://"
-  do_cmdline_cmd("augroup nvim_terminal");
-  do_cmdline_cmd("autocmd!");
-  do_cmdline_cmd("autocmd BufReadCmd " PROTO "* nested "
-                 ":if !exists('b:term_title')|call termopen( "
-                 // Capture the command string
-                 "matchstr(expand(\"<amatch>\"), "
-                 "'\\c\\m" PROTO "\\%(.\\{-}//\\%(\\d\\+:\\)\\?\\)\\?\\zs.*'), "
-                 // capture the working directory
-                 "{'cwd': expand(get(matchlist(expand(\"<amatch>\"), "
-                 "'\\c\\m" PROTO "\\(.\\{-}\\)//'), 1, ''))})"
-                 "|endif");
-  do_cmdline_cmd("augroup END");
-#undef PROTO
+  init_default_mappings();  // Default mappings.
+  TIME_MSG("init default mappings");
+
+  init_default_autocmds();
+  TIME_MSG("init default autocommands");
 
   // Reset 'loadplugins' for "-u NONE" before "--cmd" arguments.
   // Allows for setting 'loadplugins' there.