Only drop explicit xref text if xrefstyle is not set

When rewriting an interdocument xref that has explicit text (e.g., xref:page.adoc[Page Title]) to an internal xref, Assembler will drop the text if it matches the title of the target page (e.g., <<page:::>>). This can cause the link text to be unexpectedly changed (e.g., Section 2.2) if the xrefstyle attribute is set. That's because the xrefstyle kicks in when the internal xref has no explicit text. The logic in assembler should only drop the explicit text in the case that xrefstyle is not set.

If there are users who still want the current behavior to happen, it's possible we could introduce a hard override for this behavior.