fix(tests): needing two calls to setup a screen is cringe

Before calling "attach" a screen object is just a dummy container for
(row, col) values whose purpose is to be sent as part of the "attach"
function call anyway.

Just create the screen in an attached state directly. Keep the complete
(row, col, options) config together. It is still completely valid to
later detach and re-attach as needed, including to another session.

test/functional/ui/input_spec.lua

@@ -282,7 +282,6 @@ end)
 
 it('typing a simplifiable key at hit-enter prompt triggers mapping vim-patch:8.2.0839', function()
   local screen = Screen.new(60, 8)
-  screen:attach()
   command([[nnoremap <C-6> <Cmd>echo 'hit ctrl-6'<CR>]])
   feed_command('ls')
   screen:expect([[
@@ -328,7 +327,6 @@ describe('input non-printable chars', function()
   it("doesn't crash when echoing them back", function()
     write_file('Xtest-overwrite', [[foobar]])
     local screen = Screen.new(60, 8)
-    screen:attach()
     command('set shortmess-=F')
 
     feed_command('e Xtest-overwrite')
@@ -428,7 +426,6 @@ describe('display is updated', function()
   local screen
   before_each(function()
     screen = Screen.new(60, 8)
-    screen:attach()
   end)
 
   it('in Insert mode after <Nop> mapping #17911', function()