Drupal 7 date fields configured to not collect the hour/minute/second granularities can have "00" MM or DD attributes

Problem/Motivation

As shown in #2699895: Add settings to define #date_increment for datetime and datetime_range 'default' widgets, the Drupal 7 date module allowed the site builder to configure which granularity to collect:

For example, on my personal site, I have a project NodeType which has a "time range" date field that only cares about year + month granularity. Example: https://wimleers.com/work/project/cdn-far-future-expiration-drupal-7 and https://wimleers.com/work/project/ledgrid.

There are some values like 2008-00-00T00:00 and 2006-10-00T00:00 in the D7 datatabase, which cause a hard failure during migration:

Proposed resolution

Make \Drupal\migrate\Plugin\migrate\process\FormatDate::transform() detect -00-00T and -00T ISO8601 timestamps and transform to valid values.

This then results in the following DB tables in D8:

Remaining tasks

TBD

User interface changes

N/A

API changes

N/A

Data model changes

N/A

Release notes snippet

TBD