Merge support for the bar { height } option as-is from i3-gaps

related to https://github.com/i3/i3/issues/3724
related to https://github.com/i3/i3/issues/3721

In a follow-up commit, we can evolve this into the padding directive as
discussed on issue #3721.

parser-specs/config.spec

@@ -510,6 +510,7 @@ state BAR:
   'strip_workspace_numbers' -> BAR_STRIP_WORKSPACE_NUMBERS
   'strip_workspace_name' -> BAR_STRIP_WORKSPACE_NAME
   'verbose'                -> BAR_VERBOSE
+  'height'                 -> BAR_HEIGHT
   'colors'                 -> BAR_COLORS_BRACE
   '}'
       -> call cfg_bar_finish(); INITIAL
@@ -633,6 +634,10 @@ state BAR_VERBOSE:
   value = word
       -> call cfg_bar_verbose($value); BAR
 
+state BAR_HEIGHT:
+  value = number
+      -> call cfg_bar_height(&value); BAR
+
 state BAR_COLORS_BRACE:
   end
       ->