feat: support callback function in eval

[pewsheen]

What kind of change does this PR introduce?

• Bugfix
• Feature
• Docs
• New Binding issue #___
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change?

• Yes, and the changes were approved in issue #___
• No

Checklist

• When resolving issues, they are referenced in the PR's title (e.g fix: remove a typo, closes #___, #___)
• A change file is added if any packages will require a version bump due to this PR per the instructions in the readme.
• I have added a convincing reason for adding this feature, if necessary

Other information

This a draft for resolving issue #474. The API should expose to external after most of major platforms are implemented.

• Callback closure in evaluate_script should be like | val: String | { ... }.
• We will serialize the evaluated result into JSON string and pass it to the callback.
• Error from the execution result will not pass to the callback closure due to varying formats returned by each platform. I think this is a minor issue, we can deal with this later.

• TODO:
  • macOS
  • Unix
  • Windows
  • Android

Issues

[wusyong]

I think we can expose another method called evaluate_script_with_callback or something.
We can leave Android unimplemented and open an issue for it later.

[pewsheen]

I was expected to pass Result<> to the callback if an exception was thrown during the execution. However, it seems that Windows does not return an error but instead responds with the string "null" in the execution result.

It'd be best to wrap a try...catch... clause at the top level of the script if you anticipate that exceptions could occur and you want to handle it.