[WIP]3p: add localeconv tests

[johnedocampo]

Bug: 469163655

[github-actions]

🤖 Gemini Suggested Commit Message

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posix: Add NPLB tests for localeconv

Add Native Platform Abstraction Layer Benchmark (NPLB) tests for
the POSIX localeconv and uselocale functions. These tests verify
the correctness of locale-specific numeric and monetary formatting
information provided by the Starboard implementation, ensuring
compliance with POSIX standards across various locales.

Bug: 469163655

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