Fix a couple of apartment state issues (#19384)

* Fix a couple of apartment state issues

Fix for https://github.com/dotnet/coreclr/issues/17822
- The apartment state now defaults to MTA for the main thread along with a CoInitialize
- Calling `Thread.SetApartmentState` with STA now fails as expected (different behavior from previous netcore, same behavior as netfx)

Fix for https://github.com/dotnet/coreclr/issues/17787
- `WaitHandle.WaitAll` for multiple handles is not supported on an STA thread due to issues described in https://github.com/dotnet/coreclr/issues/17787#issuecomment-385117537
- It now throws `NotSupportedException` as expected (different behavior from previous netcore, same behavior as netfx)

Fix for https://github.com/dotnet/coreclr/issues/19225

* Temporarily exclude invalid CoreFX test

1 files changed, 2 insertions, 1 deletions

diff --git a/src/vm/appdomain.cpp b/src/vm/appdomain.cpp
index 47aeb103eb..63d077e4ff 100644
--- a/src/vm/appdomain.cpp
+++ b/src/vm/appdomain.cpp
@@ -3074,8 +3074,9 @@ void SystemDomain::SetThreadAptState (Thread::ApartmentState state)
         Thread::ApartmentState pState = pThread->SetApartment(Thread::AS_InSTA, TRUE);
         _ASSERTE(pState == Thread::AS_InSTA);
     }
-    else if (state == Thread::AS_InMTA)
+    else
     {
+        // If an apartment state was not explicitly requested, default to MTA
         Thread::ApartmentState pState = pThread->SetApartment(Thread::AS_InMTA, TRUE);
         _ASSERTE(pState == Thread::AS_InMTA);
     }