Deprecate $variables['page'] in taxonomy term templates

Problem/Motivation

Taxonomy module copies the same $variables['page'] pattern from node module for terms, see 📌 Deprecate $variables['page'] for node.html.twig Active for details. Once that issue is committed or RTBC, we can do a similar deprecation here and rely on the 'full' view mode.

Steps to reproduce

Proposed resolution

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet