JSON formatting support using spaces for indentation

[wenshao]

Added a new JSONWriter.Feature PrettyFormatWithSpace to format the output using spaces.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 98.72881% with 3 lines in your changes missing coverage. Please review.

Project coverage is 74.40%. Comparing base (9d3e91c) to head (a34cace).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...rc/main/java/com/alibaba/fastjson2/JSONWriter.java	97.33%	1 Missing and 1 partial ⚠️
.../alibaba/fastjson2/writer/ObjectWriterImplMap.java	85.71%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #3225      +/-   ##
============================================
+ Coverage     74.38%   74.40%   +0.02%     
- Complexity    23665    23683      +18     
============================================
  Files           668      668              
  Lines         92089    92143      +54     
  Branches      20577    20583       +6     
============================================
+ Hits          68498    68563      +65     
+ Misses        15233    15220      -13     
- Partials       8358     8360       +2     

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