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)
diff --git a/runtime/doc/eval.txt b/runtime/doc/eval.txt
index 31e901a..db74f9c 100644
--- a/runtime/doc/eval.txt
+++ b/runtime/doc/eval.txt
@@ -2801,7 +2801,9 @@
 prompt_setcallback({buf}, {expr}) none	set prompt callback function
 prompt_setinterrupt({buf}, {text}) none	set prompt interrupt function
 prompt_setprompt({buf}, {text}) none	set prompt text
-prop_add({lnum}, {col}, {props})  none	add a text property
+prop_add({lnum}, {col}, {props})  none	add one text property
+prop_add_list({props}, [[{lnum}, {col}, {end-lnum}, {end-col}], ...])
+				none	add multiple text properties
 prop_clear({lnum} [, {lnum-end} [, {props}]])
 				none	remove all text properties
 prop_find({props} [, {direction}])