Show cvNN tags in the font tweak section

These are more suitable for this than ssNN, since
they are meant for global character replacements.

gtk/gtkfontchooserwidget.c

@@ -1900,6 +1900,8 @@ update_feature_example (FeatureItem          *item,
   const char *number_formatting[] = { "zero", "nalt", "frac", NULL };
   const char *char_variants[] = {
     "swsh", "cswh", "calt", "falt", "hist", "salt", "jalt", "titl", "rand",
+    "cv01", "cv02", "cv03", "cv04", "cv05", "cv06", "cv07", "cv08", "cv09", "cv10",
+    "cv11", "cv12", "cv13", "cv14", "cv15", "cv16", "cv17", "cv18", "cv19", "cv20",
     "ss01", "ss02", "ss03", "ss04", "ss05", "ss06", "ss07", "ss08", "ss09", "ss10",
     "ss11", "ss12", "ss13", "ss14", "ss15", "ss16", "ss17", "ss18", "ss19", "ss20",
     NULL };
@@ -2133,6 +2135,8 @@ gtk_font_chooser_widget_populate_features (GtkFontChooserWidget *fontchooser)
   const char *number_formatting[] = { "zero", "nalt", "frac", NULL };
   const char *char_variants[] = {
     "swsh", "cswh", "calt", "falt", "hist", "salt", "jalt", "titl", "rand",
+    "cv01", "cv02", "cv03", "cv04", "cv05", "cv06", "cv07", "cv08", "cv09", "cv10",
+    "cv11", "cv12", "cv13", "cv14", "cv15", "cv16", "cv17", "cv18", "cv19", "cv20",
     "ss01", "ss02", "ss03", "ss04", "ss05", "ss06", "ss07", "ss08", "ss09", "ss10",
     "ss11", "ss12", "ss13", "ss14", "ss15", "ss16", "ss17", "ss18", "ss19", "ss20",
     NULL };

gtk/open-type-layout.h

@@ -29,6 +29,26 @@ static NamedTag open_type_layout_features[] = {
   { MAKE_TAG('c','p','s','p'), NC_("OpenType layout", "Capital Spacing") },
   { MAKE_TAG('c','s','w','h'), NC_("OpenType layout", "Contextual Swash") },
   { MAKE_TAG('c','u','r','s'), NC_("OpenType layout", "Cursive Positioning") },
+  { MAKE_TAG('c','v','0','1'), NC_("OpenType layout", "Character Variation 1") },
+  { MAKE_TAG('c','v','0','2'), NC_("OpenType layout", "Character Variation 2") },
+  { MAKE_TAG('c','v','0','3'), NC_("OpenType layout", "Character Variation 3") },
+  { MAKE_TAG('c','v','0','4'), NC_("OpenType layout", "Character Variation 4") },
+  { MAKE_TAG('c','v','0','5'), NC_("OpenType layout", "Character Variation 5") },
+  { MAKE_TAG('c','v','0','6'), NC_("OpenType layout", "Character Variation 6") },
+  { MAKE_TAG('c','v','0','7'), NC_("OpenType layout", "Character Variation 7") },
+  { MAKE_TAG('c','v','0','8'), NC_("OpenType layout", "Character Variation 8") },
+  { MAKE_TAG('c','v','0','9'), NC_("OpenType layout", "Character Variation 9") },
+  { MAKE_TAG('c','v','1','0'), NC_("OpenType layout", "Character Variation 10") },
+  { MAKE_TAG('c','v','1','1'), NC_("OpenType layout", "Character Variation 11") },
+  { MAKE_TAG('c','v','1','2'), NC_("OpenType layout", "Character Variation 12") },
+  { MAKE_TAG('c','v','1','3'), NC_("OpenType layout", "Character Variation 13") },
+  { MAKE_TAG('c','v','1','4'), NC_("OpenType layout", "Character Variation 14") },
+  { MAKE_TAG('c','v','1','5'), NC_("OpenType layout", "Character Variation 15") },
+  { MAKE_TAG('c','v','1','6'), NC_("OpenType layout", "Character Variation 16") },
+  { MAKE_TAG('c','v','1','7'), NC_("OpenType layout", "Character Variation 17") },
+  { MAKE_TAG('c','v','1','8'), NC_("OpenType layout", "Character Variation 18") },
+  { MAKE_TAG('c','v','1','9'), NC_("OpenType layout", "Character Variation 19") },
+  { MAKE_TAG('c','v','2','0'), NC_("OpenType layout", "Character Variation 20") },
   { MAKE_TAG('c','2','p','c'), NC_("OpenType layout", "Petite Capitals From Capitals") },
   { MAKE_TAG('c','2','s','c'), NC_("OpenType layout", "Small Capitals From Capitals") },
   { MAKE_TAG('d','i','s','t'), NC_("OpenType layout", "Distances") },