[annotations] Add linked layer option for annotation layers

[nyalldawson]

Adds a new "Linked layer" setting to the render page for annotation layers, which allows users to optionally set a linked visibility layer for the annotation layer. If set, then the annotations will only be drawn when the linked layer is visible in the map.

This is designed to mimic the similar linked layer option for the older annotation framework, in order to close the feature gap between old vs new annotations

Refs qgis/QGIS-Enhancement-Proposals#269

[qgis-bot]

@nyalldawson
This pull request has been tagged as requiring documentation.

A documentation ticket will be opened at https://github.com/qgis/QGIS-Documentation when this PR is merged.

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[qgis-bot]

@nyalldawson

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[github-actions]

🪟 Windows builds ready!

Windows builds of this PR are available for testing here. Debug symbols for this build are available here.

(Built from commit 5f4d6ff)

[qgis-bot]

@nyalldawson
A documentation ticket has been opened at qgis/QGIS-Documentation#9193
It is your responsibility to visit this ticket and add as much detail as possible for the documentation team to correctly document this change.
Thank you!