Add since info to string expressions

since is missing for string expressions (at ExpressionDescription).

SPARK-8241 ConcatWs
SPARK-16276 Elt
SPARK-1995 Upper / Lower
SPARK-20750 StringReplace
SPARK-8266 StringTranslate
SPARK-8244 FindInSet
SPARK-8253 StringTrimLeft
SPARK-8260 StringTrimRight
SPARK-8267 StringTrim
SPARK-8247 StringInstr
SPARK-8264 SubstringIndex
SPARK-8249 StringLocate
SPARK-8252 StringLPad
SPARK-8259 StringRPad
SPARK-16281 ParseUrl
SPARK-9154 FormatString
SPARK-8269 Initcap
SPARK-8257 StringRepeat
SPARK-8261 StringSpace
SPARK-8263 Substring
SPARK-21007 Right
SPARK-21007 Left
SPARK-8248 Length
SPARK-20749 BitLength
SPARK-20749 OctetLength
SPARK-8270 Levenshtein
SPARK-8271 SoundEx
SPARK-8238 Ascii
SPARK-20748 Chr
SPARK-8239 Base64
SPARK-8268 UnBase64
SPARK-8242 Decode
SPARK-8243 Encode
SPARK-8245 format_number
SPARK-16285 Sentences