vim-patch:8.1.0020: cannot tell whether a register is executing or recording

Problem:    Cannot tell whether a register is being used for executing or
            recording.
Solution:   Add reg_executing() and reg_recording(). (Hirohito Higashi,
            closes vim/vim#2745)  Rename the global variables for consistency.  Store
            the register name in reg_executing.
0b6d911e5d

src/nvim/eval.lua

@@ -236,6 +236,8 @@ return {
     pyxeval={args=1},
     range={args={1, 3}},
     readfile={args={1, 3}},
+    reg_executing={},
+    reg_recording={},
     reltime={args={0, 2}},
     reltimefloat={args=1},
     reltimestr={args=1},