Fix problem on text-width

[yasuo-ozu]

Problem

When we use multipul columns, the width of header and footer is shrinked to the column's width (as below).

Reference

columnを複数にした場合、ヘッダーとフッターが左に寄っちゃう pic.twitter.com/vhtri1D515

— yasuo_ozu@量子コンピュータエンジニア (@yasuo_ozu) January 11, 2023

[yasuo-ozu]

Limitations

When the page has some floating box, the origin point of all the columns are affect by the floating size. I think, it is the limitation of SATySFi's page-break-multicolumn primitive.

[abenori]

Thank you! Why did you introduce header-footer-context? It seems that we don't need this for fixing this bug.

[yasuo-ozu]

Thanks for comment. Before this PR, the context of document and header (or footer) is commonalized, so the header and content should have same text-width. In this PR, I split the context for content and {header, footer}. After this PR, the user with lost the way to set the context of header, so I added new config header-footer-context. But I don't think the name is so suitable fot this purpose.

[abenori]

Before this PR, the context of document and header (or footer) is commonalized, so the header and content should have same text-width.

That sounds not true. I think changing the argument to get-standard-context is sufficient as in your PR. So you don't need header-footer-context?

[abenori]

I guess we don't have to introduce a new interface header-footer-context, so I only use half of your code 3ca206c. Thank you very much.