[Debugger] Fix crash when there is a generic struct with a field that…

[UnityAlex]

… is an enumerator. (mono#12368) Unity: (case 1210416)

• [Debugger] Debugger crashes when inside a class, there is an internal struct, with a field that is an enumerator.
  files.myBucket.GetEnumerator().get_Current().Key
  Fixes mono64[80780:1186894] error: * Assertion: should not be reached at debugger-agent.c:6619 mono/mono#10735

• [Debugger] Debugger crashes when there is a generic struct with a field that is an enumerator.
  Example: files.get_Current().Key
  A unit test that reproduces this crash was added too.
  Fixes mono64[80780:1186894] error: * Assertion: should not be reached at debugger-agent.c:6619 mono/mono#10735

• Removing the extra space.

• @UnityAlex cherry-pick modification: Removed tests

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