Mesh layer remove datasetgroup

[JanCaha]

Description

Adds option to add Dataset Groups to Mesh Layer with the same name (but not from the same uri), the Dataset Group names are automatically renamed to "Original Name _Number", for clarity.

Adds option to remove Dataset Groups from Mesh Layer. Only additional Dataset Groups (not associated with mesh source file) can be removed.

Includes GUI interface:

[github-actions]

🪟 Windows builds

Download Windows builds of this PR for testing.
Debug symbols for this build are available here.
(Built from commit 62d87a7)

🪟 Windows Qt6 builds

Download Windows Qt6 builds of this PR for testing.
(Built from commit 62d87a7)

[qgis-bot]

@JanCaha
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.
Also, any commit having [needs-doc] or [Needs Documentation] in will see its message pushed to the issue, so please be as verbose as you can.

Thank you!

[qgis-bot]

@JanCaha

This pull request has been tagged for the changelog.

• The description will be harvested so please provide a "nearly-ready" text for the final changelog
• If possible, add a nice illustration of the feature. Only the first one in the description will be harvested (GIF accepted as well)
• If you can, it's better to give credits to your sponsor, see below for different formats.

You can edit the description.

Format available for credits

• Funded by NAME
• Funded by URL
• Funded by NAME URL
• Sponsored by NAME
• Sponsored by URL
• Sponsored by NAME URL

Thank you!

[uclaros]

That's some nice functionality!

[uclaros]

Some minor last const stuff (I also unresolved two previous const comments)

[qgis-bot]

@JanCaha
A documentation ticket has been opened at qgis/QGIS-Documentation#9464
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!