refactor: free more reachable memory with EXITFREE (#26349)

Discovered using __sanitizer_print_memory_profile().

src/nvim/autocmd.c

@@ -2573,6 +2573,11 @@ void do_autocmd_uienter(uint64_t chanid, bool attached)
 {
   static bool recursive = false;
 
+#ifdef EXITFREE
+  if (entered_free_all_mem) {
+    return;
+  }
+#endif
   if (starting == NO_SCREEN) {
     return;  // user config hasn't been sourced yet
   }