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/30state_pen.test b/src/libvterm/t/30state_pen.test
index d1e0d14..915baec 100644
--- a/src/libvterm/t/30state_pen.test
+++ b/src/libvterm/t/30state_pen.test
@@ -10,8 +10,8 @@
   ?pen blink = off
   ?pen reverse = off
   ?pen font = 0
-  ?pen foreground = rgb(240,240,240)
-  ?pen background = rgb(0,0,0)
+  ?pen foreground = rgb(240,240,240,is_default_fg)
+  ?pen background = rgb(0,0,0,is_default_bg)
 
 !Bold
 PUSH "\e[1m"
@@ -75,40 +75,40 @@
 
 !Foreground
 PUSH "\e[31m"
-  ?pen foreground = rgb(224,0,0)
+  ?pen foreground = idx(1)
 PUSH "\e[32m"
-  ?pen foreground = rgb(0,224,0)
+  ?pen foreground = idx(2)
 PUSH "\e[34m"
-  ?pen foreground = rgb(0,0,224)
+  ?pen foreground = idx(4)
 PUSH "\e[91m"
-  ?pen foreground = rgb(255,64,64)
+  ?pen foreground = idx(9)
 PUSH "\e[38:2:10:20:30m"
   ?pen foreground = rgb(10,20,30)
 PUSH "\e[38:5:1m"
-  ?pen foreground = rgb(224,0,0)
+  ?pen foreground = idx(1)
 PUSH "\e[39m"
-  ?pen foreground = rgb(240,240,240)
+  ?pen foreground = rgb(240,240,240,is_default_fg)
 
 !Background
 PUSH "\e[41m"
-  ?pen background = rgb(224,0,0)
+  ?pen background = idx(1)
 PUSH "\e[42m"
-  ?pen background = rgb(0,224,0)
+  ?pen background = idx(2)
 PUSH "\e[44m"
-  ?pen background = rgb(0,0,224)
+  ?pen background = idx(4)
 PUSH "\e[101m"
-  ?pen background = rgb(255,64,64)
+  ?pen background = idx(9)
 PUSH "\e[48:2:10:20:30m"
   ?pen background = rgb(10,20,30)
 PUSH "\e[48:5:1m"
-  ?pen background = rgb(224,0,0)
+  ?pen background = idx(1)
 PUSH "\e[49m"
-  ?pen background = rgb(0,0,0)
+  ?pen background = rgb(0,0,0,is_default_bg)
 
 !Bold+ANSI colour == highbright
 PUSH "\e[m\e[1;37m"
   ?pen bold = on
-  ?pen foreground = rgb(255,255,255)
+  ?pen foreground = idx(15)
 PUSH "\e[m\e[37;1m"
   ?pen bold = on
-  ?pen foreground = rgb(255,255,255)
+  ?pen foreground = idx(15)