Use QGIS processing or native reprojection tools instead of delegating to GDAL

[Guts]

Here:

gml_application_schema_toolbox/gml_application_schema_toolbox/gui/gmlas_panel_mixin.py

Line 58 in 0018469

def translate(self, params):

Use https://gis.stackexchange.com/a/316364/19817 or https://qgis.org/pyqgis/master/core/QgsCoordinateTransform.html?highlight=qgscoordinatetransform#module-QgsCoordinateTransform

Goals:

• better perfs
• avoid useless external calls to GDAL and reduce dependency

[benoitblanc]

To convert PostgreSQL data to GMLAS format, we can use ogr2ogr processing in QGIS. At the moment, this processing can only convert a single layer so I opened a PR to be able to convert a whole schema : qgis/QGIS#45955