fix: address an issue where highlight doesn't work with stacked bar plot

[dakshpokar]

Bug Report

Description

The current implementation of the stacked bar plot visualization does not support highlighting. This is however, supported for normal bar plot. We need to build a generic solution to support segmented plots.

Steps to Reproduce

1. Run example/stacked/matplotlib/example_mpl_stacked.py
2. Activate maidr
3. Check highlighting by using left/right arrow keys

Actual Behavior

Highlighting doesn't work when stacked bar plot is triggered with maidr.

Expected Behavior

Highlighting should work, as it is working for the example in maidr.js repository for stacked bar plot.