Plot content

[ManuelHentschel]

Adds a method to the api to get the content of a plot as array buffer, as suggested in REditorSupport/vscode-R#823 (comment)

I had to modify the dependencies a bit, to get fetch and Headers to work in nodejs/vscode. Not really sure, if this is the cleanest way.

Feel free to modify/ignore if you have different plans for the api.

[nx10]

Thanks for the PR. Sorry for the dependency problems, I forgot to push the latest changes yesterday.

I am not sure converting to an ArrayBuffer object is a helpful abstraction here.
With the response promise you can call .text() .json() or .arrayBuffer()` or whatever is needed in the specific case.
Do you think users will generally want to convert to an ArrayBuffer?

[ManuelHentschel]

Do you think users will generally want to convert to an ArrayBuffer?

I think it would be useful to have a method that returns only the content of a plot, without any http/ws logic (as e.g. the response type). For text-based formats it might make sense to return the text itself, but for binary formats, some type of buffer is needed for this. Buffer seems to be a bit more useful than ArrayBuffer, so i changed the return type.

[nx10]

ArrayBuffer will load the plot into memory before writing it. Keeping it as an Response object allows streaming.