Cleanup some dead paths in EH

[huoyaoyuan]

Also moves ThreadStartException to managed code.

The general question is about where RaiseException is required instead of DispatchManagedException. I played a bit with it in QCall and DispatchManagedException seems to interop directly with C++ EH on Windows. UnwindAndContinueRethrowHelperAfterCatch(nativeRethrow) is intentional, but HandleThreadAbort doesn't look like.

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[jkotas]

The test failure looks related:

  Starting:    System.Diagnostics.Process.Tests (parallel test collections = on [2 threads], stop on fail = off)
    System.Diagnostics.Tests.ProcessStartInfoTests.TestWindowStyle [SKIP]
      Condition(s) not met: "IsAdmin_IsNotNano_RemoteExecutorIsSupported"
    System.Diagnostics.Tests.ProcessStartInfoTests.Verbs_GetWithExeExtension_ReturnsExpected [SKIP]
      Condition(s) not met: "IsNotWindowsNanoServer"
    System.Diagnostics.Tests.ProcessStartInfoTests.ShellExecute_Nano_Fails_Start [FAIL]
      Assert.Throws() Failure: Exception type was not an exact match
      Expected: typeof(System.Threading.ThreadStartException)
      Actual:   typeof(System.Threading.ThreadStateException)
      ---- System.Threading.ThreadStateException : Thread has not been started.

[jkotas]

Could you please resolve the conflict?

[jkotas]

LGTM, Thanks!

@janvorli Could you please take a look as well?