fix: Changes for Deephaven UI embedding widget plugins

[mattrunyon]

These changes are needed so Deephaven UI can embed widget plugins. This also creates a difference between the widget component and the widget panel component.

Will open a companion UI plugin PR to utilize these in Deephaven UI.

Tested the panels still function as intended for grid, chart, and dataframe.

[codecov]

Codecov Report

Attention: 74 lines in your changes are missing coverage. Please review.

Comparison is base (f9f62db) 46.65% compared to head (ce9cb4f) 46.57%.

❗ Current head ce9cb4f differs from pull request most recent head 7e0a67b. Consider uploading reports for the commit 7e0a67b to get more accurate results

Files	Patch %	Lines
.../dashboard-core-plugins/src/PandasWidgetPlugin.tsx	0.00%	29 Missing ⚠️
...s/dashboard-core-plugins/src/ChartWidgetPlugin.tsx	0.00%	16 Missing ⚠️
...es/dashboard-core-plugins/src/GridWidgetPlugin.tsx	0.00%	15 Missing ⚠️
...ard-core-plugins/src/panels/PandasReloadButton.tsx	0.00%	7 Missing ⚠️
...s/dashboard-core-plugins/src/PandasPanelPlugin.tsx	33.33%	4 Missing ⚠️
packages/chart/src/Chart.tsx	0.00%	1 Missing ⚠️
...es/dashboard-core-plugins/src/ChartPanelPlugin.tsx	66.66%	1 Missing ⚠️
...ges/dashboard-core-plugins/src/GridPanelPlugin.tsx	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1644      +/-   ##
==========================================
- Coverage   46.65%   46.57%   -0.09%     
==========================================
  Files         593      597       +4     
  Lines       36467    36531      +64     
  Branches     9135     9142       +7     
==========================================
  Hits        17014    17014              
- Misses      19401    19465      +64     
  Partials       52       52              

Flag	Coverage Δ
unit	46.57% <8.64%> (-0.09%)	⬇️

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