ContainerInline with a ParentBlock has a wrong Span End

[zickb]

There is an issue with the Inline.Span.End in case of a container inline with a parent block.
Example Input: "a\n"
Expected behavior: The Span.End of the container inline should be 1.
Actual behavior: The Span.End of the container inline is 0.

Workaround (does not work trivially if #730 is hit):

if (inline is ContainerInline { ParentBlock: not null } containerInline)
    return new SourceSpan(containerInline.FirstChild?.Span.Start ?? 0, containerInline.LastChild?.Span.End ?? 0);

Related issue: #702