Add additional breaking changes / fixes of note to migration page

The following discussion from !645 (merged) should be addressed:

@mojavelinux started a discussion: (+1 comment)

Additional breaking changes / fixes:

• remove the 2-character (i.e., "") quote block syntax
• drop verse table cell style (treat as normal table cell) (asciidoctor#3111)
• apply verbatim substitutions to literal paragraphs attached to list item (asciidoctor#3205)
• always use title as xreftext if target block has an empty caption, regardless of xrefstyle value (asciidoctor#3745)
• account for empty positional attribute when parsing attrlist (asciidoctor#3813 and asciidoctor#4033)
• don’t allow AsciiDoc table cell to set document attribute that was unset from the API (exceptions include: compat-mode, toc, showtitle, and notitle) (asciidoctor#4017)
• ensure default document attributes unset in parent document remain unset in AsciiDoc table cell (asciidoctor#2586)
• use attribute, if set, as seed value for counter even if not already registered as a counter (asciidoctor#4014)
• don’t include trailing period, question mark, or exclamation point in target (URL) of autolink (asciidoctor#3860)