A pair of high-rise projects planned for the Figueroa Corridor downtown jumped into the headlines this week, as if out of nowhere. The first, set to replace the Wilshire Grand hotel and office complex at Figueroa Street and Wilshire Boulevard, will be designed by AC Martin Partners, the big local firm. It has an estimated budget of more than $1 billion. The other, proposed for a site near the southern edge of South Park, across from the Los Angeles Convention Center, is by Daniel Libeskind, best known for his Jewish Museum in Berlin and his much-altered master plan for the World Trade Center site in Lower Manhattan.