add UX to load MVT layers from style URL only

[3nids]

Vector Tiles layers can now be loaded from the style only. The data source is then automatically parsed from the style, and multiple data sources are now supported.

For instance, loading the Swisstopo base layer with multiple data sources:

Screen.Recording.2024-09-11.at.16.21.27.mov

Here are a couple of screenshots before/after:

Funded by OPENGIS.ch

[qgis-bot]

@3nids
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!

[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 7211c69)

[3nids]

@nirvn following our discussion, I move the URI update from the constructor to app. It seems more consistent and safer indeed.

[qgis-bot]

@3nids
A documentation ticket has been opened at qgis/QGIS-Documentation#9254
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]

@3nids

This pull request has been tagged for the changelog.

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