Support dictionary encoding for STRING data type.

[jt2594838]

Support dictionary encoding for STRING data type.
Move datatype-encoding map into TsFile.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 92.68293% with 3 lines in your changes missing coverage. Please review.

Project coverage is 62.33%. Comparing base (a90fe9a) to head (c9389e9).

Files with missing lines	Patch %	Lines
.../apache/tsfile/file/metadata/enums/TSEncoding.java	95.00%	2 Missing ⚠️
...che/tsfile/encoding/encoder/TSEncodingBuilder.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #238      +/-   ##
===========================================
+ Coverage    62.28%   62.33%   +0.04%     
===========================================
  Files          476      476              
  Lines        31614    31654      +40     
  Branches      4107     4107              
===========================================
+ Hits         19692    19730      +38     
- Misses       11475    11477       +2     
  Partials       447      447              

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