Convert ProgressiveStringDecoderTest to Kotlin (#37728)

Summary:
## Changelog:

[Internal] [Changed] - Convert ProgressiveStringDecoderTest to Kotlin

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Pull Request resolved: #37728

Reviewed By: cipolleschi

Differential Revision: D46552406

Pulled By: cortinico

fbshipit-source-id: 9fd75991cff98fcf71223c5bc386a7ee0b435d8d

Author: Ryan Lucas