`lang` provided under `format` key not respected when rendering books

[dragonstyle]

When the lang is specified under a format, like:

format:
  html:
    lang: zh

We don't respect that lang when rendering a book (it must instead be at the root level).

See #251

[dragonstyle]

This is resolved as of Quarto 1.3 pre-release

[dragonstyle]

Incorrect- this error is still happening as of Quarto 1.3.

[dragonstyle]

Note to self: This issue ultimately is a result of the book project context being initialized very early in the rendering process. The book project type synthesizes things like a sidebar for use in a website, and the issue with this is that the synthesized sidebar needs access to localized strings. The lang that is active for the format hasn't yet been determined (too early in the rendering process), so we look for a global lang flag and use that if present.

We'll need to defer and break up the book initialization to fix this.