patch 9.0.0887: cannot easily try out what codes various keys produce

Problem:    Cannot easily try out what codes various keys produce.
Solution:   Add a script to gather key code information, with an initial list
            of codes to compare with.
diff --git a/Filelist b/Filelist
index adfb7ea..9825e45 100644
--- a/Filelist
+++ b/Filelist
@@ -177,6 +177,8 @@
 		src/testdir/Make_all.mak \
 		src/testdir/*.in \
 		src/testdir/*.py \
+		src/testdir/keycode_check.vim \
+		src/testdir/keycode_check.json \
 		src/testdir/lsan-suppress.txt \
 		src/testdir/sautest/autoload/*.vim \
 		src/testdir/testluaplugin/lua/testluaplugin/*.lua \