feat: add default hl group for devicons (#1849)

lua/telescope/config.lua

@@ -650,7 +650,8 @@ append(
   "color_devicons",
   true,
   [[
-  Boolean if devicons should be enabled or not.
+  Boolean if devicons should be enabled or not. If set to false, the
+  "TelescopeResultsFileIcon" highlight group is used.
   Hint: Coloring only works if |termguicolors| is enabled.
 
   Default: true]]

lua/telescope/utils.lua

@@ -437,7 +437,7 @@ utils.transform_devicons = load_once(function()
       if conf.color_devicons then
         return icon_display, icon_highlight
       else
-        return icon_display
+        return icon_display, "TelescopeResultsFileIcon"
       end
     end
   else
@@ -465,7 +465,7 @@ utils.get_devicons = load_once(function()
       if conf.color_devicons then
         return icon, icon_highlight
       else
-        return icon
+        return icon, "TelescopeResultsFileIcon"
       end
     end
   else