fix: Remove emphasis from xref in headings and fix xrefs in headings

[kesara]

• This change removes emphasis on xref content in headings.
• This change also adds xref content to name when the format="none" in the xref element.
• When xref is in title, if xref has a target to a reference use square brackets ([ <target text> ]).
• If the xref target is not a reference don't use brackets or parenthesis.
• If the xref element has text content: For reference targets: <text content> [<target>] For other targets: <text content> (<target>)

Fixes #683

[kesara]

See https://github.com/ietf-tools/xml2rfc/issues/683#issuecomment-1710963089 for examples.