In addition to geometry filtered layers for each geometry
type in a mixed-geometry type layer adds a table
layer with all attributes.
Tehre is no perfetc solution here, if the layer is created
with a filter on geometrytype, the attributes are not shown
(this is probably a pre-existing bug), if the layer is added
as is, only the first geometry type is drawn.
With this implementation at least all data (attributes and
geometries) are accessible in some way.
Note that geopackage layers added by DB Manager do not show
all geometries of a mixed type layer.
Check that all parameter's values pass the validity check,
even if not returned as QgsProcessingModelChildParameterSource.
In case of list, tests that it is really a QgsProcessingModelChildParameterSource list,
and create a QgsProcessingModelChildParameterSource from the list if it is not the case
(useful for custom parameters that return lists as ParameterFieldsMapping).
This handles the test use case for layer:
Layer name: geometry2d
Geometry: Unknown (any)
Feature Count: 8
The browser tree will now show the different geometry
layers and allow them to be added in the canvas,
GeometryCollections are skipped.
The GML format often requires extra 'hand holding' in order to
get QGIS to detect it's CRS (e.g. GML files created directly
in GDAL will not have an autodetected CRS when pulled into
QGIS). This needs fixing, but as a workaround to allow
processing algorithm porting to continue we can now skip
the crs check for these layers.
because using this more consistently throughout the codebase makes it
easier to maintain code.
We also do not want to call the copy constructor on them, using pointers
just makes this more obvious. Further, casting is also something
that's commonly done on pointers and not references.
And if you want a value or a reference, just use QgsGeometry, it's meant
to be handled like this.
