Accessors for custom compression modes

[sarthakaggarwal97]

Description

Enables accessors for custom compression modes.

Issues Resolved

#88

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[sarthakaggarwal97]

@reta please take a look! Thank you :D
I've added a test for the getters, however lmk if I should remove it. I think, in general, we don't need to test the getters/accessors.

[reta]

I've added a test for the getters, however lmk if I should remove it. I think, in general, we don't need to test the getters/accessors.

@sarthakaggarwal97 sure, what is the practical reason of exposing these properties?

[sarthakaggarwal97]

@reta I'm working on a plugin which requires me to have my own implementation of the Lucene90CompressingStoredFieldsFormat to optimize on read operations.
With this implementation, I would like to add support for ZstdCompressionMode and ZstdNoDictCompressionMode which requires me to pass them as arguments, and custom-codecs package would be able to provide the compression modes out of the box while avoiding any code/implementation duplication.
I don't see any risks in exposing the compression modes via getters. Please lmk if you see any concerns.

[reta]

I don't see any risks in exposing the compression modes via getters. Please lmk if you see any concerns.

@sarthakaggarwal97 There are few issues here:

• this plugin does not publish any artifacts (at least not supposed to) besides ZIP distribution, so the way this API is consumed in unclear to me
• the exposed API should be something like

  public CompressionMode getCompressionMode() {
      return mode == ZSTD_NO_DICT ? zstdNoDictCompressionMode : zstdCompressionMode;
  }
  

[sarthakaggarwal97]

@reta yes, if we want to just fetch the compression mode, we should use the API you suggested.
I've updated the PR to now return a map of compression modes against the respective Mode.