Fix Sentry CLI MSBuild for Xamarin and NetFX

[mattjohnsonpint]

Some further testing on Xamarin and .NET Framework projects after the 3.27.0 release, found symbol uploads not working as expected.

• We can't rely on checking for a non-empty TargetFramework property, because that only exists in the newer SDK-style .NET projects. Since the intention here is to run for anything other than the outer build when multi-targeting, we can check for an empty InnerTargets property (which is only set in the case we need to exclude).

• On Xamarin Android projects, we always will need the obj folder contents rather than bin to get the correct debug files uploaded. Since the obj folder is guaranteed to always have the files we need, we should make it the default and remove the SentryIncludeIntermediateOutputPath option. (We don't need to use the bin folder at all.)