Allow Timestamp/Datetime values to use up to 6 digits of microsecond precision

[jordanw-bq]

Issue #, if available: #986

Description of changes:
Add formatter to allow for variable amount of microsecond precision (up to 6 digits)

• add additional tests around microsecond precision
• update TimeValue to align with Timestamp/Datetime changes

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 #988 (5990495) into develop (9a08770) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             develop     #988   +/-   ##
==========================================
  Coverage      99.87%   99.87%           
- Complexity      2381     2397   +16     
==========================================
  Files            234      234           
  Lines           5477     5513   +36     
  Branches         357      357           
==========================================
+ Hits            5470     5506   +36     
  Misses             5        5           
  Partials           2        2           

Impacted Files	Coverage Δ	Complexity Δ
...lasticsearch/sql/data/model/ExprDatetimeValue.java	100.00% <100.00%> (ø)	13.00 <1.00> (ø)
...forelasticsearch/sql/data/model/ExprTimeValue.java	100.00% <100.00%> (ø)	9.00 <1.00> (+1.00)
...asticsearch/sql/data/model/ExprTimestampValue.java	100.00% <100.00%> (ø)	13.00 <0.00> (ø)
...opendistroforelasticsearch/sql/expression/DSL.java	100.00% <0.00%> (ø)	132.00% <0.00%> (+3.00%)
...ticsearch/sql/ppl/parser/AstExpressionBuilder.java	100.00% <0.00%> (ø)	28.00% <0.00%> (+2.00%)
...h/sql/expression/function/BuiltinFunctionName.java	100.00% <0.00%> (ø)	3.00% <0.00%> (ø%)
...ion/operator/predicate/UnaryPredicateOperator.java	100.00% <0.00%> (ø)	23.00% <0.00%> (+10.00%)

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[chloe-zh]

Could you add integration test in sql/DateTimeFunctionIT.java for SQL (if comparison test is not applicable) and ppl/DateTimeFunctionIT.java for PPL in integ-test module? The rest LGMT, thanks!

[dai-chen]

Thanks for the fix!