This extends the existing Isolate::SetAllowCodeGenerationFromStringsCallback
mechanism, by adding SetModifyCodeGenerationFromStringCallback, which
can also modify the eval argument (it could e.g. add escaping).

Bug: chromium:940927
Change-Id: I2b72ec2e3b77a5a33f428a0db5cef3f9f8ed6ba2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1593336Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Daniel Vogelheim <vogelheim@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62185}