Unify grid metrics calculations by relying on shared logic mostly based
on values directly from the font tables, this deduplicates a lot of code
and gives us more control over how we interpret various metrics.
Also separate metrics for underlined, strikethrough, and overline
thickness and position, and box drawing thickness, so that they can
individually be adjusted as the user desires.
* font: disable default font features for Menlo and Monaco
Both of these fonts have a default ligature on "fi" which makes terminal
rendering super ugly. The easiest thing to do is special-case these
fonts and disable ligatures. It appears other terminals do the same
thing.
Not as straightforward as it sounds, but not hard either:
* Read OS/2 sfnt tables from TrueType fonts
* Calculate strikethrough position/thickness (prefer font-advertised if possible, calculate if not)
* Plumb the SGR code through the terminal state -- does not increase cell memory size
* Modify the shader to support it
The shaders are getting pretty nasty after this... there's tons of room for improvement. I chose to follow the existing shader style for this to keep it straightforward but will likely soon refactor the shaders.
