vim-patch:8.1.2304: cannot get the mouse position when getting a mouse click

Problem:    Cannot get the mouse position when getting a mouse click.
Solution:   Add getmousepos().
db3a205147

src/nvim/eval.lua

@@ -162,6 +162,7 @@ return {
     getloclist={args={1, 2}},
     getmarklist={args={0, 1}},
     getmatches={args={0, 1}},
+    getmousepos={},
     getpid={},
     getpos={args=1},
     getqflist={args={0, 1}},