Support cast function in SQL

[penghuo]

Issue #, if available: #915

Description of changes:

1. Implement cast function in SQL.
2. Update cast function doc. https://github.com/penghuo/sql/blob/support-cast/docs/user/dql/functions.rst#cast

Todo: #924, #925

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

Merging #926 (59a96dc) into develop (64c7bd6) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##             develop     #926    +/-   ##
===========================================
  Coverage      99.86%   99.86%            
- Complexity      2265     2321    +56     
===========================================
  Files            229      230     +1     
  Lines           5235     5342   +107     
  Branches         346      346            
===========================================
+ Hits            5228     5335   +107     
  Misses             5        5            
  Partials           2        2            

Impacted Files	Coverage Δ	Complexity Δ
...elasticsearch/sql/analysis/ExpressionAnalyzer.java	100.00% <100.00%> (ø)	31.00 <1.00> (+1.00)
...opendistroforelasticsearch/sql/expression/DSL.java	100.00% <100.00%> (ø)	128.00 <9.00> (+9.00)
...search/sql/expression/config/ExpressionConfig.java	100.00% <100.00%> (ø)	3.00 <0.00> (ø)
...h/sql/expression/function/BuiltinFunctionName.java	100.00% <100.00%> (ø)	3.00 <0.00> (ø)
.../expression/operator/convert/TypeCastOperator.java	100.00% <100.00%> (ø)	44.00 <44.00> (?)
...ticsearch/sql/sql/parser/AstExpressionBuilder.java	100.00% <100.00%> (ø)	50.00 <2.00> (+2.00)

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[dai-chen]

Thanks for the changes!