Add implicit page attribute to indicate page is in latest version

Add an implicit page attribute when converting the AsciiDoc documents to indicate the page is in the latest version of the page's component. If it is, this attribute is set. If it is not, the attribute is not set.

We'll need to decide how to name this attribute. There are several possibilities:

page-latest
page-component-latest
page-component-version-latest
page-version-latest

Since page-version is an alias for page-component-version, I would prefer page-component-version-latest of the two. If we want to follow the programming model, then page-component-latest would be the most fitting. I'm neutral on page-latest since it feels very ambiguous.