Ability to control the order of processing model output layers

[pathmapper]

Feature description.

There are a lot of use cases where a specific layer order for processing model output layers is wanted, e.g. so that a layer with point features is not hidden by a layer with polygon features.

Unless I'm missing something, there's currently no way to control the order of processing model output layers, so it could be that you have to rearrange the layers manually after the model is finished.

Here's a test_model_output.zip where it looks like the output order is totally random, despite the algorithm 2 is always executed after 1 by setting a dependency.

Maybe one option to control the layer order would be to make the output order dependent on the order in which the model algorithms are executed. This way it would be possible to control the layer order by setting algorithm dependencies, e.g. for the sample model above layer 2 would be always positioned on top of layer 1.

Additional context

This is a recurring question on SE:

• https://gis.stackexchange.com/questions/157702/processing-modeler-output-order
• https://gis.stackexchange.com/questions/278256/control-rendering-layer-order-of-outputs-from-qgis-3-processing-modeler
• https://gis.stackexchange.com/questions/387284/setting-layer-order-for-output-in-qgis-graphical-modeler
• https://gis.stackexchange.com/questions/377868/output-layers-order-in-qgis-graphic-modeller-algorithm-execution-order-depend

[pathmapper]

-> #52996