Split logical names in moe module

[NuojCheng]

Description

Split following logical names:

• embed_no_exp into: embed_no_exp, embed_moe
• activation_embed into: activation_embed, activation_embed_moe
• activation_length_no_exp into: activation_length_no_exp, activation_length_no_exp_moe
• activation_batch into activation, activation_batch
• activation_batch into activation_batch, activation_batch_moe
• activation_batch_no_exp into activation_batch_no_exp, activation_batch_no_exp_moe

Tests

• Pure FSDP: https://diff.googleplex.com/#key=fdiAZWeyybSP
• FSDP+TP: https://diff.googleplex.com/#key=GrrJyIf9fENe

Checklist

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• I have necessary comments in my code, particularly in hard-to-understand areas.
• I have run end-to-end tests tests and provided workload links above if applicable.
• I have made or will make corresponding changes to the doc if needed, including adding new documentation pages to the relevant Table of Contents (toctree directive) as explained in our documentation.

[codecov]

Codecov Report

❌ Patch coverage is 65.21739% with 8 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/maxtext/layers/moe.py	65.21%	8 Missing ⚠️

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