Add ref test for tab background highlighting

Generated with

    echo -e "\x1b[48;5;31m1\t2\n\n3\x1b[0;m"

tests/ref.rs

@@ -12,10 +12,7 @@ use alacritty::term::SizeInfo;
 use alacritty::ansi;
 
 macro_rules! ref_tests {
-    ($($name:ident,)*) => {
-        ref_tests!($($name),*);
-    };
-    ($($name:ident),*) => {
+    ($($name:ident)*) => {
         $(
             #[test]
             fn $name() {
@@ -28,14 +25,15 @@ macro_rules! ref_tests {
 }
 
 ref_tests! {
-    fish_cc,
-    indexed_256_colors,
-    ll,
-    tmux_git_log,
-    tmux_htop,
-    vim_large_window_scroll,
-    vim_simple_edit,
-    zsh_tab_completion,
+    fish_cc
+    indexed_256_colors
+    ll
+    tab_bg_highlight
+    tmux_git_log
+    tmux_htop
+    vim_large_window_scroll
+    vim_simple_edit
+    zsh_tab_completion
 }
 
 fn read_u8<P>(path: P) -> Vec<u8>

tests/ref/tab_bg_highlight/alacritty.recording

@@ -0,0 +1,5 @@
+%                                                                               
 
]2;jwilm@jwilm-desk: ~/code/alacritty]1;..ode/alacritty
jwilm@jwilm-desk ➜  ~/code/alacritty  [?1h=[?2004hecho -e "\x1b[48;5;31m1\t2\n\n3\x1b[0;m"echo -e "\x1b[48;5;31m1\t2\n\n3\x1b[0;m"[?1l>[?2004l
+]2;echo -e "\x1b[48;5;31m1\t2\n\n3\x1b[0;m"]1;echo1	2
+
+3
+%                                                                               
 
]2;jwilm@jwilm-desk: ~/code/alacritty]1;..ode/alacritty
jwilm@jwilm-desk ➜  ~/code/alacritty  [?1h=[?2004h

tests/ref/tab_bg_highlight/size.json

@@ -0,0 +1 @@
+{"width":644.0,"height":412.0,"cell_width":8.0,"cell_height":17.0}