patch 9.0.0683: cannot specify a time for :echowindow

Problem:    Cannot specify a time for :echowindow.
Solution:   A count can be used to specify the display time. Add
            popup_findecho().
diff --git a/src/proto/vim9instr.pro b/src/proto/vim9instr.pro
index f0298f9..87914f3 100644
--- a/src/proto/vim9instr.pro
+++ b/src/proto/vim9instr.pro
@@ -60,6 +60,7 @@
 int generate_STRINGMEMBER(cctx_T *cctx, char_u *name, size_t len);
 int generate_ECHO(cctx_T *cctx, int with_white, int count);
 int generate_MULT_EXPR(cctx_T *cctx, isntype_T isn_type, int count);
+int generate_ECHOWINDOW(cctx_T *cctx, int count, long time);
 int generate_SOURCE(cctx_T *cctx, int sid);
 int generate_PUT(cctx_T *cctx, int regname, linenr_T lnum);
 int generate_EXEC_copy(cctx_T *cctx, isntype_T isntype, char_u *line);