Granularity item processor produces unusable options set with 3.x facets exposed filters

Problem/Motivation

I recently migrated a 2.x facet that was using the granularity item processor over to the new 3.x facets exposed filters system and found that with the exact same granularity item processor settings the new facets exposed filter was producing an odd / erroneous / unusable set of options from the same Search API Solr data source.

For example, if I set a granularity of 50 and min value of 0 I used to get (with the old 2.x facet) a nice set of options like:

0-50
50-100
100-150
...

But the new facets exposed filter produces a mess like this (just a snippet - the list is huge):
0-50
1-51
1-51
2-52
2-52
2-52
3-53
3-53
4-54
...

Steps to reproduce

1. Set up a 3.x facets exposed filter atop a numeric search API field.
2. Enable the granularity item processor on this facets exposed filter.
3. View the filter and see the odd set of options produced.

Proposed resolution

TBD

Remaining tasks

Propose resolution, MR, review.

User interface changes

None.

API changes

None.

Data model changes

None.