It was previously using draw_tiled_bitmap, which always aligns the
tiles with the global origin and does not respect the alpha of the
source. Switch to a new Painter::blit_tiled helper which uses
Painter::blit under the hood, which has more correct behavior.
(...and ASSERT_NOT_REACHED => VERIFY_NOT_REACHED)
Since all of these checks are done in release builds as well,
let's rename them to VERIFY to prevent confusion, as everyone is
used to assertions being compiled out in release.
We can introduce a new ASSERT macro that is specifically for debug
checks, but I'm doing this wholesale conversion first since we've
accumulated thousands of these already, and it's not immediately
obvious which ones are suitable for ASSERT.
We'll want to remove the LibGUI dependency from the WebContent process.
This is the first basic step of removing unnecessary LibGUI includes
and swapping out GUI::Painter for Gfx::Painter.