SimulatorBase::ConvertArg should be a protect member so that
CallArgument::CallArgument can access it.

Change-Id: I60b23b45c2247cd28e73808df7b77e604d154932
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3659057Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Auto-Submit: Yu Liu <liuyu@loongson.cn>
Cr-Commit-Position: refs/heads/main@{#80693}