Preserve linewrap flag across alt screen switches

While neither VTE, URxvt nor Kitty handle this, preserving the linewrap
flag across alternate screen switches seems like the correct thing to
do. XTerm also does handle this correctly, which indicates that it is a
bug and not a feature.

alacritty_terminal/tests/ref.rs

@@ -63,6 +63,7 @@ ref_tests! {
     scroll_up_reset
     clear_underline
     region_scroll_down
+    wrapline_alt_toggle
 }
 
 fn read_u8<P>(path: P) -> Vec<u8>

alacritty_terminal/tests/ref/wrapline_alt_toggle/alacritty.recording

@@ -0,0 +1,2 @@
+%                                                                                                                                          
 

 UL  /…/tests/ref/wrapline_alt_t…  fix_newline_flag  

 UL  /…/tests/ref/wrapline_alt_t…  fix_newline_flag  [?2004hfor i in {1..$(tput cols)}; do echo -ne "a"; done && echo -ne "\e[?1049h" && echo -ne "x" && echo -ne "\e[?1049l" && echo -ne "a"for i in {1..$(tput cols)}; do echo -ne "a"; done && echo -ne "\e[?1049h" && echo -ne "x" && echo -ne "\e[?1049l" && echo -ne "a"[?2004l
+aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa[?1049hx[?1049la%                                                                                                                                          
 

 UL  /…/tests/ref/wrapline_alt_t…  fix_newline_flag  

 UL  /…/tests/ref/wrapline_alt_t…  fix_newline_flag  [?2004hexitexit[?2004l

alacritty_terminal/tests/ref/wrapline_alt_toggle/config.json

@@ -0,0 +1 @@
+{"history_size":0}

alacritty_terminal/tests/ref/wrapline_alt_toggle/size.json

@@ -0,0 +1 @@
+{"width":1259.0,"height":683.0,"cell_width":9.0,"cell_height":19.0,"padding_x":4.0,"padding_y":9.0,"dpr":1.1666666666666667}