A raw HTML string that the renderer must insert
without escaping.
Constructed via RawHtml::new (from Lombok New) or,
preferably, the unsafe_no_inline! macro which makes
the security warning loud at the call site.
The content field is pub(crate) with a public
getter (get_content), a crate-internal mut-getter,
and a crate-internal setter. The public getter lets
the renderer read the unescaped content; the
setter / mut-getter are kept crate-internal so the
content is set at construction (preferably through
unsafe_no_inline!) and not mutated after.
get_content is public — core/tests/raw, core/tests/raw_html and
macros/tests/unsafe_no_inline all read it from outside the crate.
get_mut / set stay crate-internal so the content is set at
construction and never mutated afterwards.