Regression: taxonomy.termReference.* plugins have been renamed.

From #1399080-25: Feedback on crumbs 7.x:

As a followup to 2070181, I've just found the taxonomy use-case doc and I observe that it shows plugin keys like taxonomy.termReference.field_animal_category.*, whereas the plugin keys I observe are like taxonomy.field_quux.*. Given that taxonomy.termReference.* is "disabled by default", I wonder whether this discrepancy is an error in the code and an alternative root cause of my problems in 2070181.

This is a regression, and yet another reason we need unit tests.
(currently the test coverage is really poor, and I lack the time to improve it)

We can restore this, but we need to make sure that existing configuration is not lost. hook_update_N() seems the appropriate tool for this.
I am working on it.