[SPARKNLP-957] Solves average pooling computation

[danilojsl]

Description

Solves average pooling computation when processing batches in E5 and MPNet

Motivation and Context

Solves an issue that return empty embeddings

How Has This Been Tested?

• Local Tests
• Google Colab notebook

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• Code improvements with no or little impact
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING page.
• I have added tests to cover my changes.
• All new and existing tests passed.