Vertical Bar Chart in "Normal mode" does not order split series correctly when "Descending" is selected

[swtrux]

Kibana version:
7.9.1
Elasticsearch version:
7.9.1

Server OS version:
RHEL Linux 3.10.0-1127.13.1.el7.x86_64

Browser version:
Firefox 80.0 (64-bit)

Browser OS version:
Windows 10.0.18363.0 (64-bit)

Describe the bug:
Vertical Bar Charts with a split series do not order items correctly when "Descending" or "Ascending" are selected for the "Order" in the split series. I believe this has been an issue for many versions as I can't remember when it worked correctly.

Steps to reproduce:
Create Vertical Bar Chart ordering the Buckets in Descending order, then split the series and also order it as descending. See images below for example with Metricbeat file system utilization split with mount points.

Expected behavior:
The split series should be ordered correctly. In my example the mount points should be shown ordered by percent full.

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)

[timroes]

Might be related to #14536

[flash1293]

Blocked by #86184

[stratoula]

Thank you for contributing to this issue, however, we are closing this issue due to inactivity as part of a backlog grooming effort. If you believe this feature/bug should still be considered, please reopen with a comment.