Slug History Tracking & Usage

[ssddanbrown]

Adds a purpose-built slug tracking system to note old slugs on changes, so that they can be used for lookup.
We're already doing something similar via page revisions, but this will be a more robust implementation which works for all core content types.

For #5411

Todo

• Create new table & migrate revision slug data.
• Log shelf slug changes
• Log book slug changes
• Log chapter slug changes
• Log page slug changes
• Add shelf slug handling fallback
• Add book slug handling fallback
• Add chapter slug handling fallback
• Update page slug handling fallback to use this
• Ensure child items can be looked up after parent slug change
• Add testing coverage