[MTP][Breaking] Remove TrxFullyQualifiedTypeNameProperty once we get rid of vstestProvider capability

[Youssef1313]

Once we get rid of vstestProvider capability, TestMethodIdentifierProperty should be required. This basically means that we should be able to remove TrxFullyQualifiedTypeNameProperty and instead rely on TestMethodIdentifierProperty.

[Youssef1313]

A better idea here is to make TestMethodIdentifierProperty required based on if it's needed or not. i.e, allow an extension to "ask" for it. Framework authors can then "omit" the property if not asked for. We will either also make it required always for server mode, or let the IDE ask for it somehow.