chore: raise QEMU memory and extend the FontDemo sample

Give the guest 512 MiB so the full Noto Sans SC face and the fonttools
buffers fit, and render a mixed Chinese/Latin string in FontDemo.

Apps/FontDemo/main.vp

@@ -41,7 +41,7 @@ export def _start() -> int:
     font: fonttools.Font* = fonttools.load(FONT_PATH)
     if font is not None:
         fonttools.draw_text(font, fb, CANVAS_W, CANVAS_H,
-                            TEXT_X, TEXT_BASELINE, "你好，世界", TEXT_SIZE, uint32(FG_COLOR))
+                            TEXT_X, TEXT_BASELINE, "你好，世界，Hello，World", TEXT_SIZE, uint32(FG_COLOR))
 
     root.mainloop()
     process.exit(0)

build.py

@@ -213,7 +213,7 @@ def RunQemu():
         qemu_cmd += ['-pflash', ovmf_code]
     qemu_cmd += [
         '-drive', 'file=disk.img,format=raw,if=ide',
-        '-m', '256m',
+        '-m', '512m',
         '-vga', 'std',
         '-usb',
         '-device', 'usb-kbd',