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/lua/vim_spec.lua

@@ -637,7 +637,6 @@ describe('lua stdlib', function()
     matches('big failure\nvery async', remove_trace(eval('v:errmsg')))
 
     local screen = Screen.new(60, 5)
-    screen:attach()
     screen:expect {
       grid = [[
       ^                                                            |
@@ -1403,7 +1402,6 @@ describe('lua stdlib', function()
     end)
 
     local screen = Screen.new(50, 7)
-    screen:attach()
     exec_lua([[
       timer = vim.uv.new_timer()
       timer:start(20, 0, function ()
@@ -2130,7 +2128,6 @@ describe('lua stdlib', function()
     eq({ 1, 5 }, api.nvim_win_get_cursor(0))
 
     local screen = Screen.new(60, 3)
-    screen:attach()
     eq(1, eval('v:hlsearch'))
     screen:expect {
       grid = [[
@@ -3401,7 +3398,6 @@ stack traceback:
 
     it('callback is not invoked recursively #30752', function()
       local screen = Screen.new(60, 10)
-      screen:attach()
       exec_lua([[
         vim.on_key(function(key, typed)
           vim.api.nvim_echo({
@@ -3779,7 +3775,6 @@ stack traceback:
 
     it('fails in fast callbacks #26122', function()
       local screen = Screen.new(80, 10)
-      screen:attach()
       exec_lua([[
         local timer = vim.uv.new_timer()
         timer:start(0, 0, function()
@@ -3797,7 +3792,6 @@ stack traceback:
 
   it('vim.notify_once', function()
     local screen = Screen.new(60, 5)
-    screen:attach()
     screen:expect {
       grid = [[
       ^                                                            |
@@ -3994,7 +3988,6 @@ stack traceback:
     it('updates ruler if cursor moved', function()
       -- Fixed for win_execute in vim-patch:8.1.2124, but should've applied to nvim_win_call too!
       local screen = Screen.new(30, 5)
-      screen:attach()
       exec_lua [[
         _G.api = vim.api
         vim.opt.ruler = true
@@ -4137,7 +4130,6 @@ stack traceback:
 
   it('vim.lua_omnifunc', function()
     local screen = Screen.new(60, 5)
-    screen:attach()
     command [[ set omnifunc=v:lua.vim.lua_omnifunc ]]
 
     -- Note: the implementation is shared with lua command line completion.