treewide: automatically md-convert option descriptions

the conversion procedure is simple:

 - find all things that look like options, ie calls to either `mkOption`
   or `lib.mkOption` that take an attrset. remember the attrset as the
   option
 - for all options, find a `description` attribute who's value is not a
   call to `mdDoc` or `lib.mdDoc`
 - textually convert the entire value of the attribute to MD with a few
   simple regexes (the set from mdize-module.sh)
 - if the change produced a change in the manual output, discard
 - if the change kept the manual unchanged, add some text to the
   description to make sure we've actually found an option. if the
   manual changes this time, keep the converted description

this procedure converts 80% of nixos options to markdown. around 2000
options remain to be inspected, but most of those fail the "does not
change the manual output check": currently the MD conversion process
does not faithfully convert docbook tags like <code> and <package>, so
any option using such tags will not be converted at all.

nixos/modules/hardware/opengl.nix

@@ -35,7 +35,7 @@ in
 
     hardware.opengl = {
       enable = mkOption {
-        description = ''
+        description = lib.mdDoc ''
           Whether to enable OpenGL drivers. This is needed to enable
           OpenGL support in X11 systems, as well as for Wayland compositors
           like sway and Weston. It is enabled by default
@@ -51,7 +51,7 @@ in
       driSupport = mkOption {
         type = types.bool;
         default = true;
-        description = ''
+        description = lib.mdDoc ''
           Whether to enable accelerated OpenGL rendering through the
           Direct Rendering Interface (DRI).
         '';
@@ -60,11 +60,11 @@ in
       driSupport32Bit = mkOption {
         type = types.bool;
         default = false;
-        description = ''
+        description = lib.mdDoc ''
           On 64-bit systems, whether to support Direct Rendering for
           32-bit applications (such as Wine).  This is currently only
-          supported for the <literal>nvidia</literal> as well as
-          <literal>Mesa</literal>.
+          supported for the `nvidia` as well as
+          `Mesa`.
         '';
       };
 
@@ -90,7 +90,7 @@ in
         type = types.listOf types.package;
         default = [];
         example = literalExpression "with pkgs; [ vaapiIntel libvdpau-va-gl vaapiVdpau intel-ocl ]";
-        description = ''
+        description = lib.mdDoc ''
           Additional packages to add to OpenGL drivers. This can be used
           to add OpenCL drivers, VA-API/VDPAU drivers etc.
         '';
@@ -100,9 +100,9 @@ in
         type = types.listOf types.package;
         default = [];
         example = literalExpression "with pkgs.pkgsi686Linux; [ vaapiIntel libvdpau-va-gl vaapiVdpau ]";
-        description = ''
+        description = lib.mdDoc ''
           Additional packages to add to 32-bit OpenGL drivers on
-          64-bit systems. Used when <option>driSupport32Bit</option> is
+          64-bit systems. Used when {option}`driSupport32Bit` is
           set. This can be used to add OpenCL drivers, VA-API/VDPAU drivers etc.
         '';
       };