"nvim -es": disable shada #21723

Problem:
`nvim -es` (and `nvim -Es`) is the recommended way to non-interactively
run commands/vimscript. But it enables shada by default, which is
usually not wanted.

Solution:
- Disable shada by default for `nvim -es/-Es`. This can be overridden by
  `-i foo` if needed.
- Do NOT change the 'loadplugins' default.
  - User config + packages _should_ be enabled by default, for both `nvim
    -es` and `nvim -l`. Else any Lua packages you have can't be accessed
    without `-u path/to/config`, which is clumsy.
      - Use-cases:
        ```
        nvim --headless "+Lazy! sync" +qa
            would become: nvim -es "+Lazy! sync"
        nvim --headless +PlugInstall +qall
            would become: nvim -es +PlugInstall
        ```
  - Opt-out (`--clean` or `-u NONE`) is much easier than opt-in (`-u
    path/to/config`).
  -  User config/packages are analogous to pip packages, which are
     expected when doing `python -c ...`.

related: 7c94bcd2d7
related: ddd0eb6f51

src/nvim/main.c

@@ -1228,6 +1228,9 @@ static void command_line_scan(mparm_T *parmp)
         if (exmode_active) {    // "-es" silent (batch) Ex-mode
           silent_mode = true;
           parmp->no_swap_file = true;
+          if (p_shadafile == NULL || *p_shadafile == NUL) {
+            set_option_value_give_err(kOptShadafile, STATIC_CSTR_AS_OPTVAL("NONE"), 0);
+          }
         } else {                // "-s {scriptin}" read from script file
           want_argument = true;
         }
@@ -2085,8 +2088,7 @@ static void source_startup_scripts(const mparm_T *const parmp)
 {
   // If -u given, use only the initializations from that file and nothing else.
   if (parmp->use_vimrc != NULL) {
-    if (strequal(parmp->use_vimrc, "NONE")
-        || strequal(parmp->use_vimrc, "NORC")) {
+    if (strequal(parmp->use_vimrc, "NONE") || strequal(parmp->use_vimrc, "NORC")) {
       // Do nothing.
     } else {
       if (do_source(parmp->use_vimrc, false, DOSO_NONE, NULL) != OK) {