vim-patch:8.0.1309: cannot use 'balloonexpr' in a terminal

Problem:    Cannot use 'balloonexpr' in a terminal.
Solution:   Add 'balloonevalterm' and add code to handle mouse movements in a
            terminal. Initial implementation for Unix with GUI.
51b0f3701e

src/nvim/misc1.c

@@ -602,6 +602,7 @@ int is_mouse_key(int c)
          || c == K_LEFTDRAG
          || c == K_LEFTRELEASE
          || c == K_LEFTRELEASE_NM
+         || c == K_MOUSEMOVE
          || c == K_MIDDLEMOUSE
          || c == K_MIDDLEDRAG
          || c == K_MIDDLERELEASE