Include and Display macros should generate inline content when used in an inline context

ParserUtils#convertToInline() caused regressions as it made macros inline that don't support inline mode in AllDocs. The problem there is that the include macro is used in an HTML macro where it is contained in non-inline HTML but still treated as inline macro. I've changed the implementation to really just remove the top-level paragraph if there is a single paragraph as this covers the main use case of including inline content. Otherwise, this change seems too dangerous to be backported to LTS branches.