patch 8.2.0256: time and timer related code is spread out

Problem:    Time and timer related code is spread out.
Solution:   Move time and timer related code to a new file. (Yegappan
            Lakshmanan, closes #5604)
diff --git a/src/Make_morph.mak b/src/Make_morph.mak
index bb5805c..2c226de 100644
--- a/src/Make_morph.mak
+++ b/src/Make_morph.mak
@@ -102,6 +102,7 @@
 	term.c							\
 	testing.c						\
 	textprop.c						\
+	time.c							\
 	ui.c							\
 	undo.c							\
 	usercmd.c						\