[ft] default_weights analogue for normal (grayscale) AA

[Yan Pepel]

Hi all.

I'm trying to darken/embolden fonts. I found out that people often patch
the `default_weights` const to accomplish that[1] (see src/base/ftlcdfil.c).
I've changed the const in this way:

static const FT_LcdFiveTapFilter default_weights =
               { 0x28, 0x50, 0x64, 0x50, 0x28 };

As a result LCD-antialiased fonts look just perfect on my monitor:
https://imgur.com/v8Wa63s

Now I want to darken/embolden fonts that are rendered using the normal
(grayscale) AA. How do I do that? Which const should I tweak?

[1] 
https://wiki.archlinux.org/index.php/Font_configuration#Advanced_LCD_filter_specification