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/legacy/cmdline_spec.lua

@@ -15,7 +15,6 @@ describe('cmdline', function()
   -- oldtest: Test_cmdlineclear_tabenter()
   it('is cleared when switching tabs', function()
     local screen = Screen.new(30, 10)
-    screen:attach()
 
     feed_command([[call setline(1, range(30))]])
     screen:expect([[
@@ -79,7 +78,6 @@ describe('cmdline', function()
   -- oldtest: Test_verbose_option()
   it('prints every executed Ex command if verbose >= 16', function()
     local screen = Screen.new(60, 12)
-    screen:attach()
     exec([[
       command DoSomething echo 'hello' |set ts=4 |let v = '123' |echo v
       call feedkeys("\r", 't') " for the hit-enter prompt
@@ -104,7 +102,6 @@ describe('cmdline', function()
   -- oldtest: Test_cmdline_redraw_tabline()
   it('tabline is redrawn on entering cmdline', function()
     local screen = Screen.new(30, 6)
-    screen:attach()
     exec([[
       set showtabline=2
       autocmd CmdlineEnter * set tabline=foo
@@ -121,7 +118,6 @@ describe('cmdline', function()
   -- oldtest: Test_redraw_in_autocmd()
   it('cmdline cursor position is correct after :redraw with cmdheight=2', function()
     local screen = Screen.new(30, 6)
-    screen:attach()
     exec([[
       set cmdheight=2
       autocmd CmdlineChanged * redraw
@@ -145,7 +141,6 @@ describe('cmdline', function()
 
   it("setting 'cmdheight' works after outputting two messages vim-patch:9.0.0665", function()
     local screen = Screen.new(60, 8)
-    screen:attach()
     exec([[
       set cmdheight=1 laststatus=2
       func EchoTwo()
@@ -175,7 +170,6 @@ describe('cmdline', function()
   -- oldtest: Test_cmdheight_tabline()
   it("changing 'cmdheight' when there is a tabline", function()
     local screen = Screen.new(60, 8)
-    screen:attach()
     api.nvim_set_option_value('laststatus', 2, {})
     api.nvim_set_option_value('showtabline', 2, {})
     api.nvim_set_option_value('cmdheight', 1, {})
@@ -191,7 +185,6 @@ describe('cmdline', function()
   -- oldtest: Test_rulerformat_position()
   it("ruler has correct position with 'rulerformat' set", function()
     local screen = Screen.new(20, 3)
-    screen:attach()
     api.nvim_set_option_value('ruler', true, {})
     api.nvim_set_option_value('rulerformat', 'longish', {})
     api.nvim_set_option_value('laststatus', 0, {})
@@ -218,7 +211,6 @@ describe('cmdwin', function()
       [3] = { bold = true, foreground = Screen.colors.SeaGreen }, -- MoreMsg
       [4] = { bold = true }, -- ModeMsg
     })
-    screen:attach()
     command('set more')
     command('autocmd WinNew * highlight')
     feed('q:')