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/match_spec.lua

@@ -11,7 +11,6 @@ describe('matchaddpos()', function()
   -- oldtest: Test_matchaddpos_dump()
   it('can add more than 8 match positions vim-patch:9.0.0620', function()
     local screen = Screen.new(60, 14)
-    screen:attach()
     exec([[
       call setline(1, ['1234567890123']->repeat(14))
       call matchaddpos('Search', range(1, 12)->map({i, v -> [v, v]}))
@@ -39,7 +38,6 @@ describe('match highlighting', function()
   -- oldtest: Test_match_in_linebreak()
   it('does not continue in linebreak vim-patch:8.2.3698', function()
     local screen = Screen.new(75, 10)
-    screen:attach()
     exec([=[
       set breakindent linebreak breakat+=]
       call printf('%s]%s', repeat('x', 50), repeat('x', 70))->setline(1)
@@ -55,7 +53,6 @@ describe('match highlighting', function()
 
   it('is shown with incsearch vim-patch:8.2.3940', function()
     local screen = Screen.new(75, 6)
-    screen:attach()
     exec([[
       set incsearch
       call setline(1, range(20))
@@ -82,7 +79,6 @@ describe('match highlighting', function()
 
   it('on a Tab vim-patch:8.2.4062', function()
     local screen = Screen.new(75, 10)
-    screen:attach()
     exec([[
       set linebreak
       call setline(1, "\tix")