test: nvim_ui_attach() with huge dimensions. (#5974)

Also:
- Attempt to constrain wall-of-text in screen.lua.
- Windows: Enable screen_basic_spec.lua

Closes #2180

test/functional/ui/screen_basic_spec.lua

@@ -4,8 +4,7 @@ local spawn, set_session, clear = helpers.spawn, helpers.set_session, helpers.cl
 local feed, execute = helpers.feed, helpers.execute
 local insert = helpers.insert
 local eq = helpers.eq
-
-if helpers.pending_win32(pending) then return end
+local eval = helpers.eval
 
 describe('Initial screen', function()
   local screen
@@ -690,4 +689,12 @@ describe('Screen', function()
       end)
     end)
   end)
+
+  it('nvim_ui_attach() handles very large width/height #2180', function()
+    screen:detach()
+    screen = Screen.new(999, 999)
+    screen:attach()
+    eq(999, eval('&lines'))
+    eq(999, eval('&columns'))
+  end)
 end)