fix: DH-22918: Pass ref through middleware chain, export createWidgetMiddleware helpers

[vbabich]

Plugin package changes implementing createWidgetMiddleware and createPanelMiddleware helpers, passing ref through middleware chain.

Split out of #2688

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 50.50%. Comparing base (ab2439a) to head (6390f9c).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2703      +/-   ##
==========================================
- Coverage   50.72%   50.50%   -0.23%     
==========================================
  Files         788      788              
  Lines       44923    44944      +21     
  Branches    11447    11643     +196     
==========================================
- Hits        22789    22699      -90     
- Misses      22115    22199      +84     
- Partials       19       46      +27     

Flag	Coverage Δ
unit	50.50% <100.00%> (-0.23%)	⬇️

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[Copilot]

Pull request overview

This PR updates the @deephaven/plugin middleware/panel chaining utilities to preserve Golden Layout’s state persistence by forwarding the Golden Layout ref through the panel middleware chain, and adds exported helper factories to make authoring ref-safe middleware easier.

Changes:

• Update createChainedPanelComponent to be forwardRef-based and thread the Golden Layout ref down to the base panel component.
• Tighten middleware panel typings to require ref-capable (forwardRef) panel middleware components.
• Add createPanelMiddleware / createWidgetMiddleware helper factories plus unit tests for ref-forwarding and inject/wrap behavior.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
packages/plugin/src/PluginUtils.tsx	Forward Golden Layout refs through panel middleware; add exported middleware helper factories.
packages/plugin/src/PluginUtils.test.tsx	Add/adjust tests to cover ref forwarding and the new helper factories.
packages/plugin/src/PluginTypes.ts	Tighten middleware panel typings and document the Golden Layout ref/persistence requirement.

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[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 5 comments.