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/t/10state_putglyph.test b/src/libvterm/t/10state_putglyph.test
index 5665bce..6d5d56a 100644
--- a/src/libvterm/t/10state_putglyph.test
+++ b/src/libvterm/t/10state_putglyph.test
@@ -17,6 +17,12 @@
   putglyph 0xc1 1 0,0
   putglyph 0xe9 1 0,1
 
+!UTF-8 split writes
+RESET
+PUSH "\xC3"
+PUSH "\x81"
+  putglyph 0xc1 1 0,0
+
 !UTF-8 wide char
 # U+FF10 = 0xEF 0xBC 0x90  name: FULLWIDTH DIGIT ZERO
 RESET