Fixes #9110. Fontconfig recommends different precedence for rendering
settings and generic alias settings. To comply with the recommendations,
`98-nixos.conf` has been separated into `10-nixos-rendering.conf` and
`60-nixos-generic-alias.conf`.
Details:
* The option `fonts.enableFontConfig` has (finally) been renamed
`fonts.fontconfig.enable`.
* Configurations are loaded in this order: first the Fontconfig-upstream
configuration is loaded, then the NixOS-specific font directories are
set, the system-wide default configuration is loaded, and finally the
user configuration is loaded (if enabled).
* The NixOS options `fonts.fontconfig.defaultFonts.monospace`,
`fonts.fontconfig.defaultFonts.sansSerif` and
`fonts.fontconfig.defaultFonts.serif` are added to allow setting the
default system-wide font used for these generic faces. The defaults
are the appropriate faces from the DejaVu collection because of their
comprehensive Unicode coverage, clean rendering, and excellent
legibility.
* The NixOS option `fonts.fontconfig.antialias` can be used to disable
antialiasing (it is enabled by default).
* The options `fonts.fontconfig.subpixel.rgba` and
`fonts.fontconfig.subpixel.lcdfilter` control the system-wide default
settings for subpixel order and LCD filtering algorithm,
respectively.
* `fonts.fontconfig.hinting.enable` can be used to disable TrueType font
hinting (it is enabled by default).
`fonts.fontconfig.hinting.autohint` controls the FreeType autohinter.
`fonts.fontconfig.hinting.style` controls the hint style; it is "full"
by default.
* User configurations can be disabled system-wide by setting
`fonts.fontconfig.includeUserConf = false`. They are enabled by
default so users can set Fontconfig options in the desktop environment
of their choice.
Any reasonably new version of fontconfig does search that path by default,
and setting this globally causes problems, as 2.10 and 2.11 need
incompatible configs.
Tested: slim+xfce desktop, chrootenv-ed steam.
I have no idea why we were setting the global variable;
e.g., neither Fedora nor Ubuntu does that.
Using pkgs.lib on the spine of module evaluation is problematic
because the pkgs argument depends on the result of module
evaluation. To prevent an infinite recursion, pkgs and some of the
modules are evaluated twice, which is inefficient. Using ‘with lib’
prevents this problem.
