regex: factor out single-sequence ansi_regex

Author: rwe

diff-so-fancy

@@ -27,7 +27,8 @@ my $ruler_width                = git_config("diff-so-fancy.rulerWidth", undef);
 my $git_strip_prefix           = git_config_boolean("diff.noprefix","false");
 my $has_stdin                  = has_stdin();
 
-my $ansi_color_regex = qr/(\e\[([0-9]{1,3}(;[0-9]{1,3}){0,10})[mK])?/;
+my $ansi_regex = qr/\e\[([0-9]{1,3}(;[0-9]{1,3}){0,10})[mK]/;
+my $ansi_color_regex = qr/(${ansi_regex})?/;
 my $reset_color      = color("reset");
 my $bold             = color("bold");
 my $meta_color       = "";