Fix field deduplication

[inferiorhumanorgans]

#93 actually missed the part of the code where the field itself is named. This PR ensures fields are renamed.

This is marked as a draft because I added a couple tests to define the expected behavior. Beyond making sure that this is the right shape for tests to take, the duplicate_ir_fields_should_not_collide test fails. Should deduplication happen when parsing SVD and YAML definitions or just SVDs?

[datdenkikniet]

I think we should do something similar to #134: if we want field names to be unique in the IR, we should enforce that through its API. That way we'll know that having an IR means that there are no duplicate field names, and the boundary at which we are still "allowed" to have them (in the SVD, or in YAML files, or during a transform) is obvious and we can easily error out or do the transformation at that boundary.

If we don't do that, we should not do field deduplication in the IR at all, and we should rely on DeleteFields and AddFields transforms added by users instead.