Convert breadcrumbs.less to CSS

For a performance improvement, we should convert breadcrumbs.less to a CSS.

Most of the variables are breadcrumb colors that should have a CSS equivalent. The separator is injected with `content: "@

"`, which needs a CSS variable holding a quoted string. There is also a call to the `.text-smaller` mixin, which stays in type.less, so it will need to be replaced with its CSS rules or an HTML class.