patch 8.0.1639: libvterm code lags behind master

Problem:    Libvterm code lags behind master.
Solution:   Sync to head, solve merge problems.
diff --git a/src/libvterm/doc/seqs.txt b/src/libvterm/doc/seqs.txt
index e5372d0..c26dc44 100644
--- a/src/libvterm/doc/seqs.txt
+++ b/src/libvterm/doc/seqs.txt
@@ -151,6 +151,7 @@
       DECSM 1000       = Mouse click/release tracking
       DECSM 1002       = Mouse click/release/drag tracking
       DECSM 1003       = Mouse all movements tracking
+      DECSM 1004       = Focus in/out reporting
       DECSM 1005       = Mouse protocol extended (UTF-8) - not recommended
       DECSM 1006       = Mouse protocol SGR
       DECSM 1015       = Mouse protocol rxvt