rename `select_where_possible` and `select_all_or_error`
r? `@lcnr`
I find that people get confused by what these methods do. The verb "select" is not really that helpful and is just a reference to somewhat of an implementation detail of the trait solvers that doesn't even apply to most obligation kinds.
I went with `try_evaluate_obligations` and `evaluate_obligations_error_on_ambiguity`. This maintains consistency with the new solvers `evalute_goal` entry point. it's unfortunate that we say obligations rather than goals but this maintains consistency with `register_obligation` functions which I think is a good thing. In the long term possibly we rename `Obligation` or `Goal` 🤷♀️
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