feat(plugin): add MultiPlugin type for registering multiple plugins from one module

[mofojed]

• Add MULTI_PLUGIN to PluginType enum
• Define MultiPlugin interface with plugins: Plugin[] property
• Add isMultiPlugin() type guard
• Update loadModulePlugins() to flatten MultiPlugin inner plugins
• Update PluginsBootstrap to handle MultiPlugin in core plugins
• Rename PluginModule to PluginModuleExport (with deprecated alias)
• Add tests for MultiPlugin type guard and loading
• Tested using the dashboard resolve plugin branch: https://github.com/mofojed/deephaven-plugins/tree/DH-21757-homescreen-resolve
  • Ensured that the WidgetPlugin and the DashboardPlugin were both registered
  • Ensured widget data saved with the dashboard was opened like it used to, while opening deephaven.ui components open with the new mechanism

[dgodinez-dh]

Looks like some checks are failing, but it doesn't look like anything major.

[codecov]

Codecov Report

❌ Patch coverage is 48.38710% with 16 lines in your changes missing coverage. Please review.
✅ Project coverage is 49.76%. Comparing base (767f784) to head (e257ccc).
⚠️ Report is 10 commits behind head on main.

Files with missing lines	Patch %	Lines
packages/app-utils/src/plugins/PluginUtils.tsx	0.00%	9 Missing ⚠️
...ages/app-utils/src/components/PluginsBootstrap.tsx	20.00%	4 Missing ⚠️
packages/plugin/src/PluginTypes.ts	82.35%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2641      +/-   ##
==========================================
+ Coverage   49.51%   49.76%   +0.24%     
==========================================
  Files         774      774              
  Lines       43781    43860      +79     
  Branches    11263    11291      +28     
==========================================
+ Hits        21680    21828     +148     
+ Misses      22055    21986      -69     
  Partials       46       46              

Flag	Coverage Δ
unit	49.76% <48.38%> (+0.24%)	⬆️

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