[pp-1] Convert Template Preprocess hooks to OOP equivalent

Problem/Motivation

This has to happen after either:
📌 Explicitly register template_preprocess callbacks in hook_theme() Postponed
or
📌 Handle module preprocess functions Active

Either of those approaches will provide an alternative to template_preprocess_HOOK

Steps to reproduce

N/A

Proposed resolution

Convert them to the appropriate new system.

Remaining tasks

-

User interface changes

N/A

Introduced terminology

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API changes

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Data model changes

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Release notes snippet

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