vim-patch:8.1.1631: displaying signs is inefficient

+ support for neovim's dynamic width signcolumn

Problem:    Displaying signs is inefficient.
Solution:   Avoid making multiple calls to get information about a placed
            sign. (Yegappan Lakshmanan, closes #4586)

src/nvim/sign_defs.h

@@ -33,16 +33,25 @@ struct signlist
     signlist_T *prev;       // previous entry -- for easy reordering
 };
 
+/// Sign attributes. Used by the screen refresh routines.
+typedef struct sign_attrs_S {
+    int     typenr;
+    char_u *text;
+    int     texthl;
+    int     linehl;
+    int     numhl;
+} sign_attrs_T;
+
+#define SIGN_SHOW_MAX 9
+
 // Default sign priority for highlighting
 #define SIGN_DEF_PRIO 10
 
-// type argument for buf_getsigntype() and sign_get_attr()
+// type argument for sign_get_attr()
 typedef enum {
-  SIGN_ANY,
   SIGN_LINEHL,
-  SIGN_ICON,
-  SIGN_TEXT,
   SIGN_NUMHL,
+  SIGN_TEXT,
 } SignType;