patch 8.2.0674: some source files are too big

Problem:    Some source files are too big.
Solution:   Move text formatting functions to a new file. (Yegappan
            Lakshmanan, closes #6021)
diff --git a/src/Make_morph.mak b/src/Make_morph.mak
index d326174..43414e7 100644
--- a/src/Make_morph.mak
+++ b/src/Make_morph.mak
@@ -103,6 +103,7 @@
 	tag.c							\
 	term.c							\
 	testing.c						\
+	textformat.c						\
 	textobject.c						\
 	textprop.c						\
 	time.c							\