[ui][map layers] Introduce grouped style categories copy/pasting UX

[nirvn]

Description

This PR adds a couple of grouped categories shortcuts in the layer tree menu's copy / paste style sub-menu. This allows for users to rapidly copy/paste a set of grouped categories across layers.

Screenshot time:

@nyalldawson , while coding this, I noticed the labeling style category was missing for raster layer. It's been addressed here too:

[github-actions]

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[DelazJ]

Thanks @nirvn
What could also be nice (food for thought) is a "custom" entry opening a widget that would let you check the specific categories you are interested in.

[nirvn]

@DelazJ , the objective of this PR was to speed up workflows. I think your idea isn't bad at all, but outside of this scope :)

[qgis-bot]

@nirvn

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[qgis-bot]

@nirvn
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]

@nirvn
A documentation ticket has been opened at qgis/QGIS-Documentation#10068
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