lualoader: Steamroll the box-drawing

• Add drawer.frame_styles to map out the kinds of characters we need for the different loader_menu_frame values
• Respect loader_menu_frame, default to double[*]
• (imp) Use loader.printc instead of print- print adds a newline to the output, which is not the right thing we want to be doing.
• (imp) Draw horizontal frames a little more efficiently- setting the cursor after every line segment is horribly inefficient, especially on serial consoles. Halve the number of characters written at the expense of an additional loop to draw the bottom frame, which is likely more efficient in the long run for some of less ideal scenarios.

• menu.4th(8) claims that the default here was single, but unset

loader_menu_frame yielded double and we didn't have any overrides in the
default loader.conf(5), so double it is.