TreeView: Update parent selection on item click in multi-selection mode

[henon]

Description

Follow-up to #8948

Alters the hierarchic behavior of multi-select treeview toward the expected behavior. Clicking child items will automatically alter
the selection state of their parents for consistency because clicking the parent also alters the selection state of its children.

Before this change clicking children did not update the selection state of their parent(s)

How Has This Been Tested?

A unit test was adapted to check this behavior

Type of Changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation (fix or improvement to the website or code docs)

Checklist

• The PR is submitted to the correct branch (dev).
• My code follows the code style of this project.
• I've added relevant tests.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.48%. Comparing base (28bc599) to head (97a69a6).
Report is 191 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #8957      +/-   ##
==========================================
+ Coverage   89.82%   90.48%   +0.65%     
==========================================
  Files         412      419       +7     
  Lines       11878    12210     +332     
  Branches     2364     2385      +21     
==========================================
+ Hits        10670    11048     +378     
+ Misses        681      627      -54     
- Partials      527      535       +8     

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