Support multiple prop names for cdata wrapping

[mohas]

Currently cdataPropName only accepts a single key, but in many cases for example in rss we have title and description that both needs to be wrapped, so it is reasonable (and required with rss for example) to be able to use an array of keys for this prop.
see rss of bbc: https://feeds.bbci.co.uk/news/rss.xml

[github-actions]

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[mohas]

figured it out:

instead of:

type RssChannel = {
  title: string
}

made it into:

type RssChannel = {
  title: CData
}
type CData = {
  wrappedValue: string
}

let channel = {
title: {wrappedValue: 'something'}

new Response(new XMLBuilder({
      cdataPropName: 'wrappedValue',
    })