refactor: DH-23209: WidgetLoaderUtils now exported from dashboard-core-plugins

[mofojed]

• There are other cases where we just want to get the plugin for a given widget, and don't want to use a WidgetLoaderPlugin
• Export the logic so it can be reused

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 51.16%. Comparing base (897f79d) to head (f177ae2).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2729      +/-   ##
==========================================
- Coverage   51.39%   51.16%   -0.24%     
==========================================
  Files         796      797       +1     
  Lines       45746    45852     +106     
  Branches    11868    11906      +38     
==========================================
- Hits        23510    23458      -52     
- Misses      22190    22375     +185     
+ Partials       46       19      -27     

Flag	Coverage Δ
unit	51.16% <100.00%> (-0.24%)	⬇️

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