fix: disallow removing extmarks in on_lines callbacks (#23219)

fix(extmarks): disallow removing extmarks in on_lines callbacks

decor_redraw_start (which runs before decor_providers_invoke_lines) gets
references for the extmarks on a specific line. If these extmarks are
deleted in on_lines callbacks then this results in a heap-use-after-free
error.

Fixes #22801

src/nvim/api/deprecated.c

@@ -172,7 +172,7 @@ Integer nvim_buf_set_virtual_text(Buffer buffer, Integer src_id, Integer line, A
   decor.priority = 0;
 
   extmark_set(buf, ns_id, NULL, (int)line, 0, -1, -1, &decor, true,
-              false, kExtmarkNoUndo);
+              false, kExtmarkNoUndo, NULL);
   return src_id;
 }