patch 8.2.4713: plugins cannot track text scrolling

Problem:    Plugins cannot track text scrolling.
Solution:   Add the WinScrolled event. (closes #10102)
diff --git a/src/proto/autocmd.pro b/src/proto/autocmd.pro
index d8145df..366d7aa 100644
--- a/src/proto/autocmd.pro
+++ b/src/proto/autocmd.pro
@@ -26,6 +26,7 @@
 int has_textyankpost(void);
 int has_completechanged(void);
 int has_modechanged(void);
+int has_winscrolled(void);
 void block_autocmds(void);
 void unblock_autocmds(void);
 int is_autocmd_blocked(void);