Feat/sb compatible

[Lo1nt]

Make StringBuilder and StringBuffer compatible under jdk 8 and jdk11+

[codecov]

Codecov Report

Attention: 101 lines in your changes are missing coverage. Please review.

Comparison is base (8158da2) 28.47% compared to head (d7b917f) 28.75%.

Additional details and impacted files

@@            Coverage Diff             @@
##              3.x     #107      +/-   ##
==========================================
+ Coverage   28.47%   28.75%   +0.28%     
==========================================
  Files         171      173       +2     
  Lines       11731    11864     +133     
  Branches     2114     2134      +20     
==========================================
+ Hits         3340     3412      +72     
- Misses       8044     8091      +47     
- Partials      347      361      +14     

Files	Coverage Δ
...cho/hessian/io/AbstractFieldAdaptorSerializer.java	73.46% <80.00%> (+0.29%)	⬆️
...sian/io/throwable/StackTraceElementSerializer.java	66.10% <70.00%> (-0.57%)	⬇️
.../java/com/caucho/hessian/io/SerializerFactory.java	81.26% <27.27%> (-1.86%)	⬇️
...ho/hessian/io/AbstractStringBuilderSerializer.java	14.63% <14.63%> (ø)
.../hessian/io/AbstractStringBuilderDeserializer.java	18.46% <18.46%> (ø)

... and 4 files with indirect coverage changes

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[EvenLjj]

LGTM