Roslyn 5 changes (from 4.14) #3539
Description
This issue is mostly a PSA for those that use latest code from our repository that extension pattern detection is broken for latest lowering in Roslyn 5.
#3530 we already knew from the spec that ExtensionMarkerAttribute is coming, and it is there now https://github.com/icsharpcode/ILSpy/actions/runs/16934497769
Additional change: ROS casts in expression trees.
To be fixed once VSnext and Roslyn 5 are available.