Fix unavailable style-categories listed in qml-file

[signedav]

Short: On loading a stylecategorymodel the last used category selection is passed to it. Since categories from vector layers can divert to categories from raster layers, this leaded to weird info in the qml-files. This change only passes the categories that the target layer allows (crops them).

When changing a layer, the previously stored or loaded category-selection is taken over.

This is nice and makes sense on layer with the same type. On other types it don't mind that much, but are neither useful.

Anyway, the problem was, that with this in the styleCategories in the qml-file style categories where listed, that did not even exist for that layer type.

<qgis version="3.40.0-Bratislava" styleCategories="Symbology|Symbology3D|Labeling|Fields|Forms|Actions|Diagrams|GeometryOptions|Relations|Legend">

Not that bad, because there was no more content of them (since the writeSymbology methods are all layer-type-specific overrides) but still it's confusing.

So I decide that on taking over the lastStyleCategories in the model they are "cropped" to the possible style categories according to the Categories-List of the layer type.

This leads to the situation that when storing styles of raster and then open the dialog for a vector, the categories that are available in the vector layers but not in the rasters are disabled. IMO a behavior that is acceptable.

[github-actions]

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(Built from commit 70b1274)