Provide a log context on log routes

Problem/Motivation

Having an entity context available makes it easier to access the "current" entity for context aware plugins: https://www.drupal.org/docs/drupal-apis/plugin-api/plugin-contexts

This effectively prevents duplication of the code that checks and loads an entity from route parameters. A practical example of this would be creating a block that is only displayed when a log entity is provided in the current page context.

Drupal core provides a context provider for both node and taxonomy term routes:

• https://git.drupalcode.org/project/drupal/-/blob/9.4.x/core/modules/node...
• https://git.drupalcode.org/project/drupal/-/blob/9.4.x/core/modules/taxo...

There has been talk of making these core implementations more generic and be provided for all entity types (I saw @pcambra suggest this somewhere but can't find it now). I think this is a good idea in the long run but lets implement one ourselves now.

Related issues:

• #3210666: Add a base class, or possibly deriver for entity route contexts
• #3138465: Add a generic entity route context

Steps to reproduce

N/A

Proposed resolution

Mimic the drupal core node/term route context.

Remaining tasks

Implement.

User interface changes

None.

API changes

None.

Data model changes

None.