patch 8.2.0804: libvterm code lags behind the upstream version

Problem:    Libvterm code lags behind the upstream version.
Solution:   Include revision 727, but add the index instead of switching
            between RGB and indexed.
diff --git a/src/libvterm/t/64screen_pen.test b/src/libvterm/t/64screen_pen.test
index f1ee639..3a78140 100644
--- a/src/libvterm/t/64screen_pen.test
+++ b/src/libvterm/t/64screen_pen.test
@@ -29,27 +29,27 @@
 
 !Foreground
 PUSH "\e[31mG\e[m"
-  ?screen_cell 0,6 = {0x47} width=1 attrs={} fg=rgb(224,0,0) bg=rgb(0,0,0)
+  ?screen_cell 0,6 = {0x47} width=1 attrs={} fg=idx(1) bg=rgb(0,0,0)
 
 !Background
 PUSH "\e[42mH\e[m"
-  ?screen_cell 0,7 = {0x48} width=1 attrs={} fg=rgb(240,240,240) bg=rgb(0,224,0)
+  ?screen_cell 0,7 = {0x48} width=1 attrs={} fg=rgb(240,240,240) bg=idx(2)
 
 !EL sets reverse and colours to end of line
 PUSH "\e[H\e[7;33;44m\e[K"
-  ?screen_cell 0,0  = {} width=1 attrs={R} fg=rgb(224,224,0) bg=rgb(0,0,224)
-  ?screen_cell 0,79 = {} width=1 attrs={R} fg=rgb(224,224,0) bg=rgb(0,0,224)
+  ?screen_cell 0,0  = {} width=1 attrs={R} fg=idx(3) bg=idx(4)
+  ?screen_cell 0,79 = {} width=1 attrs={R} fg=idx(3) bg=idx(4)
 
 !DECSCNM xors reverse for entire screen
 PUSH "\e[?5h"
-  ?screen_cell 0,0  = {} width=1 attrs={} fg=rgb(224,224,0) bg=rgb(0,0,224)
-  ?screen_cell 0,79 = {} width=1 attrs={} fg=rgb(224,224,0) bg=rgb(0,0,224)
+  ?screen_cell 0,0  = {} width=1 attrs={} fg=idx(3) bg=idx(4)
+  ?screen_cell 0,79 = {} width=1 attrs={} fg=idx(3) bg=idx(4)
   ?screen_cell 1,0  = {} width=1 attrs={R} fg=rgb(240,240,240) bg=rgb(0,0,0)
 PUSH "\e[?5\$p"
   output "\e[?5;1\$y"
 PUSH "\e[?5l"
-  ?screen_cell 0,0  = {} width=1 attrs={R} fg=rgb(224,224,0) bg=rgb(0,0,224)
-  ?screen_cell 0,79 = {} width=1 attrs={R} fg=rgb(224,224,0) bg=rgb(0,0,224)
+  ?screen_cell 0,0  = {} width=1 attrs={R} fg=idx(3) bg=idx(4)
+  ?screen_cell 0,79 = {} width=1 attrs={R} fg=idx(3) bg=idx(4)
   ?screen_cell 1,0  = {} width=1 attrs={} fg=rgb(240,240,240) bg=rgb(0,0,0)
 PUSH "\e[?5\$p"
   output "\e[?5;2\$y"