loader: Fix boot menu on BIOS

Only the gfx-enabled boot loader supports unicode. Otherwise, we have to
use the old cons25 / ibmpc upper code page drawing characters. Check to
see if we have the gfx.term_drawbox function. If we do, we support the
unicode drawing characters. If we don't, then we have an older loader
that doesn't support it *OR* we have the reduced function, text-only
boot loader. In either of those cases, we need to use the old graphics
characters. Abstract all those details into core.hasUnicode function.

PR: 282465
MFC After: 2 day
Sponsored by: Netflix
Differential Revision:	https://reviews.freebsd.org/D47403

stand/lua/core.lua

@@ -543,6 +543,15 @@ function core.nextConsoleChoice()
 	end
 end
 
+-- The graphical-enabled loaders have unicode drawing character support. The
+-- text-only ones do not. We check the old and new bindings for term_drawrect as
+-- a proxy for unicode support, which will work on older boot loaders as well
+-- as be future proof for when we remove the old binding. This also abstracts
+-- out the test to one spot in case we start to export this notion more directly.
+function core.hasUnicode()
+	 return gfx.term_drawrect ~= nil or loader.term_drawrect ~= nil
+end
+
 -- Sanity check the boot loader revision
 -- Loaders with version 3.0 have everything that we need without backwards
 -- compatible hacks. Warn users that still have old versions to upgrade so

stand/lua/drawer.lua

@@ -506,23 +506,45 @@ drawer.frame_styles = {
 		top_right	= "+",
 		bottom_right	= "+",
 	},
-	["single"] = {
+}
+
+if core.hasUnicode() then
+	-- unicode based framing characters
+	drawer.frame_styles["single"] = {
 		horizontal	= "\xE2\x94\x80",
 		vertical	= "\xE2\x94\x82",
 		top_left	= "\xE2\x94\x8C",
 		bottom_left	= "\xE2\x94\x94",
 		top_right	= "\xE2\x94\x90",
 		bottom_right	= "\xE2\x94\x98",
-	},
-	["double"] = {
+	}
+	drawer.frame_styles["double"] = {
 		horizontal	= "\xE2\x95\x90",
 		vertical	= "\xE2\x95\x91",
 		top_left	= "\xE2\x95\x94",
 		bottom_left	= "\xE2\x95\x9A",
 		top_right	= "\xE2\x95\x97",
 		bottom_right	= "\xE2\x95\x9D",
-	},
-}
+	}
+else
+	-- non-unicode cons25-style framing characters
+	drawer.frame_styles["single"] = {
+		horizontal	= "\xC4",
+		vertical	= "\xB3",
+		top_left	= "\xDA",
+		bottom_left	= "\xC0",
+		top_right	= "\xBF",
+		bottom_right	= "\xD9",
+        }
+	drawer.frame_styles["double"] = {
+		horizontal	= "\xCD",
+		vertical	= "\xBA",
+		top_left	= "\xC9",
+		bottom_left	= "\xC8",
+		top_right	= "\xBB",
+		bottom_right	= "\xBC",
+	}
+end
 
 function drawer.drawscreen(menudef)
 	-- drawlogo() must go first.