Add tests for downgrading assembly resolution via resolution extensions

[vitek-karas]

Currently it's possible to override the default assembly resolution mechanism and resolve a reference for A, Version=3.0 with A, Version=1.0, but only via extension mechanisms (AppDomain event handler, AssemblyLoadContext event handler, or custom ALC).

Normal runtime resolution (from the ALC.Default/TPA) will now allow downgrades.

We don't seem to have any tests for this though. The closest I could find are the binder tracing tests which validate that in this case the event handlers are invoked, but it doesn't validate that if the handler returns a lower version the runtime will accept it.

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Issue Details

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Currently it's possible to override the default assembly resolution mechanism and resolve a reference for A, Version=3.0 with A, Version=1.0, but only via extension mechanisms (AppDomain event handler, AssemblyLoadContext event handler, or custom ALC).

Normal runtime resolution (from the ALC.Default/TPA) will now allow downgrades.

We don't seem to have any tests for this though. The closest I could find are the binder tracing tests which validate that in this case the event handlers are invoked, but it doesn't validate that if the handler returns a lower version the runtime will accept it.

Author:	vitek-karas
Assignees:	-
Labels:	test-enhancement, area-AssemblyLoader-coreclr
Milestone:	-