patch 9.0.0772: the libvterm code is outdated

Problem:    The libvterm code is outdated.
Solution:   Include libvterm changes from revision 790 to 801.
diff --git a/src/libvterm/t/65screen_protect.test b/src/libvterm/t/65screen_protect.test
index 718f853..ec412a5 100644
--- a/src/libvterm/t/65screen_protect.test
+++ b/src/libvterm/t/65screen_protect.test
@@ -4,13 +4,13 @@
 !Selective erase
 RESET
 PUSH "A\e[1\"qB\e[\"qC"
-  ?screen_chars 0,0,1,3 = 0x41,0x42,0x43
+  ?screen_row 0 = "ABC"
 PUSH "\e[G\e[?J"
-  ?screen_chars 0,0,1,3 = 0x20,0x42
+  ?screen_row 0 = " B"
 
 !Non-selective erase
 RESET
 PUSH "A\e[1\"qB\e[\"qC"
-  ?screen_chars 0,0,1,3 = 0x41,0x42,0x43
+  ?screen_row 0 = "ABC"
 PUSH "\e[G\e[J"
-  ?screen_chars 0,0,1,3 = 
+  ?screen_row 0 = ""