add macOS glyph adjustment options

[fenetikm]

I was still seeing issues with FiraCode on macOS so I added in a few more options to allow tweaking it.

Added options:

• macos_adjust_glyph_scale
• macos_adjust_glyph_y
• macos_adjust_glyph_x

For me, setting the scale to 0.1 and setting the glyph_y to -6.0 makes everything look right again (at a font size of 15.0).

I haven't added anything regarding documentation / changes - is that something to leave for you @kovidgoyal if you accept this? happy to do what needs to be done if you can let me know.

My specific issue was reported here: https://github.com/kovidgoyal/kitty/issues/2022

[fenetikm]

actually, there is a problem with this and that is that now the underline isn't positioned correctly. sigh need either an option for that or to adjust it relative to the above.

[kovidgoyal]

y adjustment should happen to the underline position as well, and the strikethrough position. But really, the question is why is this necessary at all. And can it be automated. For example, by drawing a selection of glyphs from the font, checking if the bottom of glyphs like g or y is too high and adjusting.

[fenetikm]

yeah, I don't like this manual adjustment either - I'll look a bit more into what Core Text can tell me.