patch 8.2.3356: adding many text properties requires a lot of function calls

Problem:    Adding many text properties requires a lot of function calls.
Solution:   Add the prop_add_list() function. (Yegappan Lakshmanan,
            closes #8751)

runtime/doc/usr_41.txt

@@ -1161,6 +1161,7 @@ Prompt Buffer:					*promptbuffer-functions*
 
 Text Properties:				*text-property-functions*
 	prop_add()		attach a property at a position
+	prop_add_list()		attach a property at multiple positions
 	prop_clear()		remove all properties from a line or lines
 	prop_find()		search for a property
 	prop_list()		return a list of all properties in a line