vim-patch:8.2.0924: cannot save and restore a register properly

Problem:    Cannot save and restore a register properly.
Solution:   Add getreginfo() and make setreg() accept a dictionary. (Andy
            Massimino, closes vim/vim#3370)
bb861e293e

Cherry-pick eval.txt changes for getreginfo() from:
6aa57295cf
207f009326

src/nvim/ops.h

@@ -90,6 +90,13 @@ typedef struct yankreg {
   dict_T *additional_data;  ///< Additional data from ShaDa file.
 } yankreg_T;
 
+/// Modes for get_yank_register()
+typedef enum {
+  YREG_PASTE,
+  YREG_YANK,
+  YREG_PUT,
+} yreg_mode_t;
+
 /// Convert register name into register index
 ///
 /// @param[in]  regname  Register name.