Font rendering differences

[sbaildon]

I'm using Apple's SF Mono as my terminal font; kitty's rendering is different from Apple's, and I'm wondering if I can get parity with Terminal.app

~ $ kitty +list-fonts --psnames

SF Mono
    SF Mono Medium (SFMono-Medium)
    SF Mono Regular (SFMono-Regular)

Here's Terminal.app with SF Mono Regular, 11

Here's kitty with SF Mono Regular, 11 (kitty -o "font_family=SFMono-Regular")

And for posterity, here's TextEdit.app with font rendering matching Apple's own Terminal.app

I've toyed with macos_thicken_font, but it's certainly not as sharp as Apple's rendering—notice the feet of 1 and 2, and the stem in the b

Terminal.app reference

kitty reference (kitty -o "font_family=SFMono-Regular" -o "font_size=11" -o "macos_thicken_font=0.4")

[page-down]

Using macos_thicken_font only increases the width of the text strokes, instead it becomes a little bit blurry.
It cannot increase the sharpness.

I noticed this problem when I started using kitty for the first time, and still don't know how to adjust CoreText / CoreGraphics / OpenGL GLSL to achieve the similar rendering result.

The following PR is also related to text rendering
#3308