patch 8.2.0660: the search.c file is a bit big

Problem:    The search.c file is a bit big.
Solution:   Split off the text object code to a separate file. (Yegappan
            Lakshmanan, closes #6007)
diff --git a/src/proto.h b/src/proto.h
index 0115c68..d54936c 100644
--- a/src/proto.h
+++ b/src/proto.h
@@ -223,6 +223,7 @@
 #  include "textprop.pro"
 # endif
 # include "testing.pro"
+# include "textobject.pro"
 # include "time.pro"
 # include "ui.pro"
 # include "undo.pro"