patch 9.0.1684: Update libvterm to rev 839

Problem: libvterm slightly outdated
Solution: Update libvterm from rev 818 to rev 839

Notable fix: libvterm now handles DECSM/DECRM with multiple arguents,
so several ncurses programs (e.g. nnn) can enable mouse properly when
run in Vim's terminal in XTerm.

closes: #12746

Signed-off-by: Christian Brabandt <cb@256bit.org>
Co-authored-by: zeertzjq <zeertzjq@outlook.com>
diff --git a/src/libvterm/t/25state_input.test b/src/libvterm/t/25state_input.test
index 4eb4c6a..11013ed 100644
--- a/src/libvterm/t/25state_input.test
+++ b/src/libvterm/t/25state_input.test
@@ -148,7 +148,9 @@
 FOCUS OUT
 
 !Focus reporting enabled
+WANTSTATE +p
 PUSH "\e[?1004h"
+  settermprop 9 true
 FOCUS IN
   output "\e[I"
 FOCUS OUT