ConditionalClassAttribute throws in cases where ConditionalFact/ConditionalTheory do not throw #7439

Last week, @jozkee and I I worked on this PR and this PR in which we added unit tests that had to create symbolic links.

Some operating systems are unable to create symlinks: iOS, Android, tvOS and Browser. This is why I had to add a Conditional* attribute that would call the method CanCreateSymbolicLinks.

The CanCreateSymbolicLinks method tries to create a symbolic link in the current OS, and returns false if it was unable to do so.

There are two different places where we define a CanCreateSymbolicLinks method, but they both do exactly the same work: FileSystemWatcherTest and FileSystemTest (which then calls MountHelper).

Initially, we both decided to add ConditionalClass on top of our new test classes, but our CI runs failed in the aforementioned operating systems, because System.Diagnostics.Process is not supported:

System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation.
 ---> System.PlatformNotSupportedException: Operation is not supported on this platform.
   at System.Diagnostics.Process.StartCore(ProcessStartInfo startInfo) in System.Diagnostics.Process.dll:token 0x6000105+0xe
   at System.Diagnostics.Process.Start() in System.Diagnostics.Process.dll:token 0x60000de+0xab
   at System.IO.Tests.FileSystemWatcherTest.CreateSymLink(String targetPath, String linkPath, Boolean isDirectory) in System.IO.FileSystem.Watcher.Tests.dll:token 0x6000129+0x8c

I decided to fix my tests by changing ConditionalClass for ConditionalFact and ConditionalTheory (see here) and the CI passed. This tells me that ConditionalFact and ConditionalTheory are wrapped by a large try catch that returns false if an exception is thrown.

@jozkee decided to fix the CanCreateSymbolicLinks method he's consuming by checking the OS, and if it's unsupported, return false. While I think this fix is fine to get him unblocked, I think this is just a workaround and not a fix to the actual problem.

Since we own ConditionalClass in this repo, can it be fixed to also try catch all exceptions and return false?