Run tests / Fix IsNetCore and IsNativeAOT for single-file apps without AOT (#2799) * Fix IsNetCore check for single-file apps without AOT, and IsNativeAOT check. * Handle TryGetVersion for single-file exe in netcoreapp3.x. * Simplify some checks. * Get version from FrameworkDescription. * Don't include confusing FrameworkDescription in netcoreapp2.x. * Rename GetVersionFromFrameworkDescription.

Run tests / Fix IsNetCore and IsNativeAOT for single-file apps without AOT (#2799) * Fix IsNetCore check for single-file apps without AOT, and IsNativeAOT check. * Handle TryGetVersion for single-file exe in netcoreapp3.x. * Simplify some checks. * Get version from FrameworkDescription. * Don't include confusing FrameworkDescription in netcoreapp2.x. * Rename GetVersionFromFrameworkDescription. #1496