patch 9.1.1669: Vim script: no support for URI de-/encoding

Problem:  Vim script: no support for URI de-/encoding
          (ubaldot)
Solution: Add the uri_encode() and uri_decode() functions
          (Yegappan Lakshmanan)

fixes: #17861
closes: #18034

Signed-off-by: Yegappan Lakshmanan <yegappan@yahoo.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/doc/version9.txt

@@ -41788,6 +41788,8 @@ Functions: ~
 |str2blob()|		convert a List of strings into a blob
 |test_null_tuple()|	return a null tuple
 |tuple2list()|		turn a Tuple of items into a List
+|uri_decode()|		URI-decode a string
+|uri_encode()|		URI-encode a string
 |wildtrigger()|		trigger wildcard expansion