Support MySQL CAST_TIME/CAST_DATE/CAST_DATETIME function

[csynineyang]

转换需求：非标准格式时间字符串转成标准格式时间字符串

cast_time.go
cast_time_test.go
解析格式（分割符固定为冒号）：
1）+-D hhh:mm:ss.ms，+-D hhh:mm.ms，+-D hhh.ms
2）+-hhh:mm:ss.ms，+-hhh:mm.ms
3）+-hhhmmss.ms，+-mmss.ms，+-ss.ms
统一输出：
+-hhh:mm:ss

cast_date.go
cast_date_test.go
解析格式（分割符为任意个非字母数字符号）：
1）YY-MM-DD, YYYY-MM-DD
2）YYYYMMDD, YYMMDD
统一输出：
YYYY-MM-DD

cast_datetime.go
cast_datetime_test.go
解析格式（分割符为任意个非字母数字符号）：
1）YYYY-MM-DD hh:mm:ss.ms, YY-MM-DD hh:mm:ss.ms
2）YYYYMMDDhhmmss.ms, YYMMDDhhmmss.ms
统一输出：
YYYY-MM-DD hh:mm:ss

排除Carbon函数库，理由是：函数库支持对标准时间格式进行各类加减和比较运算，不符合需求

[codecov-commenter]

Codecov Report

Base: 35.82% // Head: 36.95% // Increases project coverage by +1.12% 🎉

Coverage data is based on head (9c083ca) compared to base (e037f9a).
Patch coverage: 87.24% of modified lines in pull request are covered.

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #606      +/-   ##
==========================================
+ Coverage   35.82%   36.95%   +1.12%     
==========================================
  Files         195      198       +3     
  Lines       21659    22145     +486     
==========================================
+ Hits         7759     8183     +424     
- Misses      13006    13053      +47     
- Partials      894      909      +15     

Impacted Files	Coverage Δ
pkg/runtime/function/cast_time.go	85.20% <85.20%> (ø)
pkg/runtime/function/cast_date.go	88.00% <88.00%> (ø)
pkg/runtime/function/cast_datetime.go	88.62% <88.62%> (ø)

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[dongzl]

ref #569 #568 #570

[jjeffcaii]

Please fix