refactor(tests): all screen tests should use highlights

This is the first installment of a multi-PR series significantly
refactoring how highlights are being specified.

The end goal is to have a base set of 20 ish most common highlights,
and then specific files only need to add more groups to that as needed.

As a complicating factor, we also want to migrate to the new default
color scheme eventually. But by sharing a base set, that future PR
will hopefully be a lot smaller since a lot of tests will be migrated
just simply by updating the base set in place.

As a first step, fix the anti-pattern than Screen defaults to ignoring
highlights. Highlights are integral part of the screen state, not
something "extra" which we only test "sometimes". For now, we still
allow opt-out via the intentionally ugly

  screen._default_attr_ids = nil

The end goal is to get rid of all of these eventually (which will be
easier as part of the color scheme migration)

test/functional/editor/mark_spec.lua

@@ -420,12 +420,12 @@ describe('named marks view', function()
     feed("<C-w>p'a")
     screen:expect([[
                   |
-      ~           |*3
-      [No Name]   |
+      {1:~           }|*3
+      {2:[No Name]   }|
       6 line      |
       ^7 line      |
       8 line      |
-      {MATCH:.*marks} |
+      {3:<itor-marks }|
                   |
       ]])
   end)
@@ -453,7 +453,7 @@ describe('named marks view', function()
     command('bwipe!')
     screen:expect([[
       ^            |
-      ~           |*4
+      {1:~           }|*4
                   |
     ]])
     command('rshada!')