[CoreCLR] Setting RunAOTCompilation in project file runs MonoAOTCompiler even with CoreCLR runtime #11068

A customer ran into a problem where their app failed to build after switching from Mono to CoreCLR. The cause was <RunAOTCompilation>true</RunAOTCompilation> in their Directory.Build.props.

We should make sure that Mono-related targets are skipped when the runtime is CoreCLR.

Ideally, we should also warn when a Mono-specific property is used in the project configuration. These properties should be removed by the developers or at least guarded with Condition="'$(UseMonoRuntime)' == 'true'".