Clean up hook implementations in the Taxonomy module

Problem/Motivation

Hooks should be updated to match grouping standards in [meta] Standardize and clean up hook classes in core.

Steps to reproduce

n/a

Proposed resolution

Split out the TaxonomyHooks class, making theme and help new single hook classes, and entity actions a new grouped hook class.

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet