Improve error handling for creating valkyrie collections

[elrayle]

Description

The new collection instance was being set to the results of the validation failure when it failed and to false when the transactions failed.

WAS:

@collection =
          form.validate(params[collection_params]) &&
          transactions['change_set.create_collection']
          ...
         .call(form).value_or { return after_create_error }

Now, the form validation is processed before setting @collection. If a failure occurs, the process is aborted and calls after_create_errors. Likewise, if there is a failure during the transaction process, after_create_errors is called to process the error and redisplay the new form.

NOTE: This PR also moves after and before methods for create to private, deprecating the public versions. Again, this is consistent with the pattern used in works.

Follow-on work

Need to do the same for updates. This will be done in a separate PR to keep this one easier to review.

Related work

The approach is based on the same change that was made for works in PR #5448.

@samvera/hyrax-code-reviewers

[cjcolvar]

Looks great!