Respect layer/project vert datum in identify results

[nyalldawson]

When a vector layer and the project have vertical datums present, and they differ, then include the transformed Z value for the identified features in the project's datum too.

[qgis-bot]

@nyalldawson

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[github-actions]

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(Built from commit 4522e71)

[qgis-bot]

@nyalldawson
A documentation ticket has been opened at qgis/QGIS-Documentation#9291
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!

[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.

Please update the description (not the comments) with helpful description and screenshot to help the work from documentors.
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