vim-patch:8.1.1071: cannot get composing characters from the screen

Problem:    Cannot get composing characters from the screen.
Solution:   Add screenchars() and screenstring(). (partly by Ozaki Kiichi,
            closes vim/vim#4059)
2912abb3a2

src/nvim/eval.lua

@@ -290,9 +290,11 @@ return {
     rubyeval={args=1},
     screenattr={args=2},
     screenchar={args=2},
+    screenchars={args=2},
     screencol={},
     screenpos={args=3},
     screenrow={},
+    screenstring={args=2},
     search={args={1, 4}},
     searchcount={args={0,1}},
     searchdecl={args={1, 3}},