keyword in Python, so this value was previously inaccessible to PyQGIS
scripts
Also change all references to Qgis::MessageLevel values to their
fully qualified names, to ease a future transition to an enum
class (when sip bugs are fixed)
Fixes#42996
Avoids the need to remove const from all the QgsReadWriteContext
references used throughout QGIS XML loading just to be able to
push warning messages to the context.
for QgsVectorLayer, when constructing a layer with a URI which
may be invalid
These may be used for layers where the geometry type/CRS is
known in advance, and where the layer path may not be
initially resolvable. (E.g. layers with a URI pointing to a
non-existant file). It is only ever used if the layer cannot
be resolved, otherwise the actual layer geometry type will be
detected and used for the layer.
