vim-patch:8.1.0519: cannot save and restore the tag stack

Problem:    Cannot save and restore the tag stack.
Solution:   Add gettagstack() and settagstack(). (Yegappan Lakshmanan,
            closes vim/vim#3604)
f49cc60aa8

src/nvim/eval.lua

@@ -142,6 +142,7 @@ return {
     gettabinfo={args={0, 1}},
     gettabvar={args={2, 3}},
     gettabwinvar={args={3, 4}},
+    gettagstack={args={0, 1}},
     getwininfo={args={0, 1}},
     getwinposx={},
     getwinposy={},
@@ -268,6 +269,7 @@ return {
     setreg={args={2, 3}},
     settabvar={args=3},
     settabwinvar={args=4},
+    settagstack={args={2, 3}},
     setwinvar={args=3},
     sha256={args=1},
     shellescape={args={1, 2}},