[WIP] fix exp inaccuracies on complex inputs

[nurmukhametov]

📝 Summary of Changes

The previous implementation of complex exponential had numerical accuracy issues. The current one follows StableHLO exponential implementation to fix them, see here

🚀 Kind of Contribution 🐛 Bug Fix

🧪 Tests

• xla/tests/complex_unary_op_samples.h: Regenerated to include inputs and expected outputs for exp
• xla/tests/generate_complex_unary_op_samples.py: Updated to generate exp test data
• xla/tests/complex_unary_op_test.cc: Added ExpTest

[i-chaochen]

Thanks! will be best to targeting 0.7.1 and upstream, and we have a main-mirror for upstream.