bug fixed for smartMatchField, #3312

[ZivYan]

原先在抽取下划线的时候把大小写转化也处理掉了，应该是大小写转化是必须的，抽取下划线才是非必须的

[codecov-commenter]

Codecov Report

Merging #3316 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##             master    #3316   +/-   ##
=========================================
  Coverage     80.37%   80.38%           
- Complexity     7408     7412    +4     
=========================================
  Files           157      157           
  Lines         27797    27799    +2     
  Branches       6685     6686    +1     
=========================================
+ Hits          22343    22345    +2     
- Misses         3436     3437    +1     
+ Partials       2018     2017    -1     

Impacted Files	Coverage Δ	Complexity Δ
...json/parser/deserializer/JavaBeanDeserializer.java	78.63% <100.00%> (ø)	314.00 <0.00> (ø)
...main/java/com/alibaba/fastjson/util/FieldInfo.java	86.44% <100.00%> (ø)	94.00 <0.00> (ø)
...main/java/com/alibaba/fastjson/util/TypeUtils.java	78.52% <100.00%> (+0.02%)	631.00 <0.00> (+3.00)
...com/alibaba/fastjson/serializer/SerialContext.java	82.69% <0.00%> (-3.85%)	21.00% <0.00%> (-1.00%)
...java/com/alibaba/fastjson/parser/ParserConfig.java	80.67% <0.00%> (+0.14%)	226.00% <0.00%> (+1.00%)
...n/java/com/alibaba/fastjson/util/JavaBeanInfo.java	86.88% <0.00%> (+0.16%)	213.00% <0.00%> (+1.00%)

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