Refactor Google Translate response handling to use JsonNode.

[miurahr]

Removed nested static classes and replaced the response parsing logic with JsonNode for improved flexibility and reduced complexity. Updated translation extraction to handle null checks more effectively and ensure robust error handling.

Pull request type

• Other (describe below)
  refactor

Which ticket is resolved?

What does this PR change?

• Fix the following SpotBugs errors

M V EI_EXPOSE_REP EI: org.omegat.machinetranslators.google.Google2Translate$Data.getTranslations() may expose internal representation by returning Google2Translate$Data.translations At Google2Translate.java:[line 306]	
M V EI_EXPOSE_REP2 EI2: org.omegat.machinetranslators.google.Google2Translate$Data.setTranslations(List) may expose internal representation by storing an externally mutable object into Google2Translate$Data.translations At Google2Translate.java:[line 310]	
M V EI_EXPOSE_REP EI: org.omegat.machinetranslators.google.Google2Translate$Response.getData() may expose internal representation by returning Google2Translate$Response.data At Google2Translate.java:[line 286]	
M V EI_EXPOSE_REP2 EI2: org.omegat.machinetranslators.google.Google2Translate$Response.setData(Google2Translate$Data) may expose internal representation by storing an externally mutable object into Google2Translate$Response.data At Google2Translate.java:[line 290]

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