System.IO.Tests.File_Copy tests failing on Browser wasm

[jozkee]

Triggered by #40753.

First:

      [FAIL] System.IO.Tests.File_Copy_str_str_b.CopyFileWithData(data: [], readOnly: False)
      Assert.InRange() Failure
      Range:  (08/14/2020 23:38:44 - 08/14/2020 23:38:46)
      Actual: 08/14/2020 22:38:45
         at System.IO.Tests.File_Copy_str_str.CopyFileWithData(Char[] data, Boolean readOnly)
         at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)

Second (this is a new test just added on #40753):

      [FAIL] System.IO.Tests.File_Copy_Single.EnsureThrowWhenCopyToNonSharedFile
      Assert.Throws() Failure
      Expected: typeof(System.IO.IOException)
      Actual:   (No exception was thrown)
         at System.IO.Tests.File_Copy_Single.EnsureThrowWhenCopyToNonSharedFile()
         at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture)

[mdh1418]

At first glance it looks like EnsureThrowWhenCopyToNonSharedFile does not throw an error on wasm because flock is not yet implemented on emscripten emscripten-core/emscripten#11797.
Because there is only one process on WASM, locking would not work.