Add new GREL jsoup function "data()" to support HTML <script> and <style> tag data extraction

[thadguidry]

Data does not only exist in HTML or XML TextNode's but also in <script> and <style> nodes.
Useful JSON data is also sometimes contained in <script type="application/json"> as well as JSON-LD data in <script type="application/ld+json">
Jsoup provides a different method data() for working with Elements that are a DataNode for handling the contents of style, script tags etc, where contents of those tags do not show with TextNode's text() - our GREL htmlText()

Proposed solution

1. Add support for jsoup's data() functionality for Element's as defined at https://jsoup.org/apidocs/org/jsoup/nodes/Element.html#data()
2. data() will operate similarly to our existing htmlText() for TextNode's but instead work with DataNodes

Alternatives considered

Manually parsing based on root element and splitting the entire document as a single string

Additional context

1. Example tests of data() are here.
2. :containsData() is already available currently from within our GREL select() function.
3. parseJson() should be immediately applicable to parse the JSON data string.
   Ex. value.parseHtml().select("script")[2].data().parseJson().sitecore.context